PART II. GUNNERY INSTRUCTIONS
Page Chapter 1. Oerlikon 20-mm. gun 70-119 Section A. General 70-71 Section B. Group 1 71-80 Section C. Group 2 80-87 Section D. Magazine interlock 87-90 Section B. Recoiling parts 90-94 Section F. Magazine 94-103 Section G. Maintenance 103-107 Section H. Partial stripping 110-115 Section I. Care 115-118 Section J. Complete stripping 118-122 Section K. Mount 122-125 Section L. Ammunition 126-127 Section M. General information on 20 mm 127-129 Chapter 2. .50 cal., air-cooled, M-2 Basic 130-151 Section A. General 130-132 Section B. Functioning 132-136 Section C. Stripping and adjustments 137-140 Section D. Care and cleaning 146-147 Section E. Stoppages 147-151 Chapter 3. .45 sub-machine gun 152-166 Section A. General 152-153 Section B. Stripping 153-158 Section C. Care and cleaning 159-161 Section D. Functioning 161-164 Section E. Stoppages 164 Section F. Accessories 164-165 Section G. Safety precautions 166 Chapter 4. .30 cal. rifle 167-180 Section A. General and operation 161-171 Section B. Precautions 171 Section C. Stripping 172-175 Section D. Care 175-179 Section E. Remarks 180 Chapter 5. .45 cal.automatic pistol 181-192 Section A. General 181 Section B. Description 181-186 Section C. Stripping 186-188 Section D. Operation 188-191 Section E. Remarks 191-192 Chapter 6. Mk. XVIII torpedo tubes 193-201 Chapter 7. Mk. XIX torpedo tubes 202-205 Section A. General 202-204 Section B. Preparing tube for firing 204 Section C. Safety precautions 204-205 Section D. Loading 205-206 Chapter 8. Bell aircraft mount 207-209 Chapter 9. Depth charges 210-228 Chapter 10. Depth charge racks 229-232 Chapter 11. Smoke screen generator, Mk. 2 233-245 Chapter 12. Smoke screen generators, PM type 246-247 Appendix 2. 248-270
Notes on torpedoes, routine upkeep, preliminary and final adjustments, preparation of warheads and exercise heads, treatment of torpedoes after run, maintenance of other equipment.
OERLIKON 20-MM. A.A. GUN
SECTION A. GENERAL DESCRIPTION
1. The Oerlikon is primarily a close-range high-angle A. A. gun. It can be used against surface vessels, but a . 50-caliber machine gun can be used with better success against landing forces, etc. Against dive bombers the 20-mm. is an excellent gun.
2. The major difference between this gun and others is that the force of the explosion is absorbed in checking and reversing the forward motion of a relatively heavy bolt, or breechblock, that is never locked. In most guns the force of the explosion is taken by the locked breechblock and by the recoil cylinders and mechanism.
3. Firing.--This gun fires in automatic only, which means that the gun will fire as long as the trigger is pressed and there is ammunition in the magazine. When the last round of each magazine is loaded into the gun the trigger mechanism is returned automatically to the cocked position regardless of the position of the trigger. This feature prevents the breechblock mass from counterrecoiling on an empty gun after the last round is fired and, because there is no explosion to reverse the breechblock, a recocking by hand would be necessary before firing could be continued. A safe fire lever is fitted close to the right handgrip. The rate of fire is approximately 450 rounds per minute.
The magazine is easily and quickly changed. It is retained by lugs on its fore end and a magazine catch at the rear.
The gun and mount consists of three major assemblies:
4. Gun.--The gun consists of all that part of the weapon (except the magazine and cradle) that rotates about the trunnion bearing axis.
The gun may be considered in three sections.
1. Barrel, mounted in the breech casing. The breech casing is mounted in the cradle. The cradle is considered to be part of mount.
2. The various stops and locking gear together with the trigger group, all mounted in the breech casing.
Note.--The above two groups do not recoil.
3. Parts that do recoil. The breech block and bolt with the striker pin, the breech bars and springs, and the barrel spring with its casing.
5. Magazine.--The ammunition is supplied from a magazine that holds 60 rounds. The magazine is detachably mounted on the gun. It is filled and also serviced while removed from gun.
6. Mount.--The mount extends from the cradle, in which the gun is fixed, to the pedestal bolted to the deck. The cradle rotates about the trunnion axis. The mount permits the height of the gun trunnion above the deck to be altered easily and rapidly for any sight angle to suit the convenience of the gunlayer. This is done by the column-raising handwheel mounted on the pedestal head.
1. Barrel.--The barrel is a forged steel piece 4 feet inches in length, bored out to a caliber of 20 mm. or approximately 0. 8 inch. There are nine grooves in the barrel. The outside of the center section has fins that support the barrel springs, holding these springs away from the barrel and permitting air circulation for cooling. The first 2 inches of the muzzle bore flares outwards as a flash shield.
The barrel can be removed easily and quickly and another barrel substituted, without disassembly of other parts. Interrupted thrust collars machined on the barrel secure it to the
breech, casing. The barrel is assembled from the front with its interrupted thrust collars in the unlocked position. The barrel is then locked by rotating it 60° clockwise (looking from
Figure 1. Barrel locking rings.
the muzzle toward the breech). Assembly marks are provided. (See fig. 1). The barrel is prevented from accidental unlocking by the barrel locking gear described later.
The barrel is removed by rotating the barrel-locking handle into the position marked "Unlock." Rotate the barrel approximately
60° counterclockwise (looking from the muzzle to the breech) and pull out to the front (asbestos gloves are provided with the tools and spare parts to remove a hot barrel).
Note.--The clearances between the barrel and its housing in the breech casing have to be very small; therefore, a barrel may feel tight. A special tool is provided for rotating the barrel.
2. Barrel locking gear.--The barrel locking gear consists of three parts:
- Barrel locking handle pinned to--
- An axis bolt (upon which the double loading stop is free to rotate).
- Barrel locking lever, attached to the axis bolt.
Figure 2. Barrel locking gear.
The purpose of the barrel-locking gear is to prevent the barrel from rotating and thereby freeing itself from the interrupted thrust collars during the firing of the gun.
The barrel-locking handle carries a catch lever that moves a pin, holding the barrel-locking handle in either of two positions, "Locked" or "Unlocked. " When the catch lever is pressed in toward the breech casing, and the handle is moved from "Unlocked" to "Locked," the axis is turned, thereby rotating the barrel-locking lever into a slot in the barrel. This locks the barrel so that it cannot rotate about its own axis. (See fig. 2.)
A stop pin is mounted in the left side of the breech casing and engages a slot in the rear end of the barrel.
When inserting a barrel and rotating it into place, the stop pin positions the barrel so that the locking lever can be engaged in its barrel slot; by turning the locking handle. (See fig. 3.)
The stop pin also serves to stop the rotation of the barrel in the opposite direction, so that the interrupted collars are in position to permit withdrawal of the barrel from the breech casing.
The double loading stop prevents loading a round of ammunition
Figure 3. Barrel stop pin.
into the barrel unless the chamber is already clear at the double loading; stop. A hole is drilled through the top wall of the Chamber of the barrel, and in this hole the double loading stop plunger operates. The operation of the double loading stop is described later on.
3. Breech casing.--The breech casing is a steel forging, bored but longitudinally, and, its chief functions are to:
- Carry the barrel at its front end.
- Carry the trigger group at its rear end.
- Act as a guideway for the breech block which recoils, and returns to the firing position, with a reciprocating motion.
- Carry the magazine on its top.
- Attach to the mount.
The gun is secured to the cradle of the mount by:
- Two shoes that are a part of the breech casing (located at the front and rear) and fit into keyways in the cradle.
- A gun securing bolt in the cradle which enters into a corresponding recess in the front shoe of the casing and takes the main fore and aft thrust on firing.
When gun is being mounted in the cradle, the inside of the securing bolt hole in the breech casing and the securing bolt itself should be thoroughly greased for protection against corrosion.
4. Magazine catch gear and ejector.--Magazine catch gear and ejector is mounted in the breech casing and consists of three sections.
- Catch gear to retain the magazine in position.
- Front portion of the magazine interlock gear.
The magazine catch gear is operated by a magazine catch lever (a) (see fig. 4) rotating on an axis bolt (1) mounted oh the casing. A front toe (n) on this lever engages with a face on the ejector (e). A rear toe (m) on this lever engages with the upper rear end of the ejector. The ejector (e) is free to move slightly in a longitudinal direction and therefore can be moved to the fear by rotating the magazine catch lever (a) toward the muzzle,
The ejector normally tends to move to the front because of the pressure of the magazine catch spring. However, the ejector can be held cocked to the rear, by the magazine catch (p). The magazine catch is pivoted at the rear and is able to rise in front, tends to force the catch into engagement with the front end of the ejector.
On the front end at the top of the ejector is a lug (b) that engages a corresponding lug (o) on the magazine and holds the magazine to the gun. If the ejector is held cocked to the rear by the catch, the lug is clear of the magazine so that the latter
Figure 4.--Magazine catch gear and ejector.
can be shipped or unshipped. The ejector can be moved rearward to the cocked position by rotating the magazine catch lever toward the muzzle.
When the magazine is shipped, the ejector is moved forward automatically, into position for locking the magazine. A projection on the magazine pushes down the front ends of the catch, disengaging it and allowing the ejector to move forward under the influence of the catch spring, into position to lock the magazine.
The catch may be disengaged without the necessity of shipping a magazine by pressing down the forward ends of the catch, using any suitable tool.
CAUTION.--When shipping a magazine the catch gear must be in the cocked position. The magazine securing lug on the ejector is back of the front end of the catch. No attempt should be made to cock the gear by forcing a magazine past the lug.
5. Double loading stop operation. (See figs. 5-8).--The purpose of the double-loading stop gear is to make it impossible for the breech block to counterrecoil and load a round into the firing chamber unless the chamber is already empty. This avoids the jam that would occur if the rear end of a cartridge case had been torn away, leaving a portion of the case jammed in the firing chamber.
The double loading stop (d) with its operating lever (c), upper plunger (b) and lower plunger (a) are shown in the position they occupy when the gun is cocked. The double loading stop plunger (a) is projecting into the chamber and is the end actuated by the cartridge case. This lower plunger (a) lifts the upper plunger (b) against the rear toe of the double-loading stop operating lever (c) lowering its front end, this permits the double-loading stop to rotate about its axis under the pressure of its springs (f). The double-loading stop (a) acts as a catch to hold the bolt mass to the rear.
The front end of the double-loading stop (d) is raised by spring (f) and the rear end has fallen until it is in the path of the stop plates mounted one on each breech bar.
The left breech bar recoils to the rear carrying with it the stop plate marked "l" (on the right breech bar the stop plate is marked "r"). The rear end of the stop plates is sloped to lift the double-loading stop against the pressure of its springs. The springs assert themselves after the hardened stop plates have passed the double-loading stop. Faces on the rear end of the double-loading stop (r) then intercept the hardened stop plates on the breech bars as the breech bars counterrecoil and thereby hold the whole recoiling mass to the rear.
When the gun is operating normally the fired cartridge case is ejected before the breech bars have recoiled far enough to reach the double-loading stop (d). When ejection of the fired cartridge case occurs, the double-loading stop lower-plunger (a) is no longer held outward by the cartridge case and the whole system is then returned to its inward position by the spring under the double-loading stop lever (c).
Interception of the breech bars by the stop plates on breech bars intercepting the double-loading stop (d) occurs only if a
Figure 5. Double loading stop gear.
A--Double loading stop plunger, lower; B--double loading stop plunger, upper; C--double lkoading stop lever; D--double loading stop; E--double loading sdtop guide busing; F--double loading stop spring.
Figure 6. Double loading stop gear. Gun has fired and cartridge is in firing chamber.
Figure 7. Double loading stop gear. Part of cartridge shell left in chamber as recoil takes place.
C--Double loading stop lever; D--double loading stop.
Figure 8. Double loading stop gear. Counterrecoil is arrested by the stop plate bearing against the double loading stop.
C--Double loading stop lever; D--double loading stop.
portion of the fired cartridge case remains in the chamber in line with plunger (a).
The double-loading stop plunger (a) is shaped to lie flush with the curve of the firing chamber wall. This lower plunger (a) has a shoulder on its outer end that prevents it from turning and also limits the travel of the lower plunger. The upper plunger (b) is limited on its inward travel by a shoulder on the guide bushing (e) and on its outward travel by the rear end of operating lever (c).
Note.--The double-loading stop operates in the event of a torn cartridge case being left in the chamber and in contact with the lower plunger. If the portion of the torn cartridge case left in the chamber is forward of the stop, the double-loading stop will not operate and a jam will occur.
SECTION C. TRIGGER FUNCTION
The chief function of the trigger group is that a trigger hook (a, fig. 9) mounted on the breech casing (b) (a nonrecoiling part) can hook onto the recoiling sear (d) that is on the end of the breech bolt (e) and thereby hold the recoiling mass in the cocked position (fig. 9).
Further features are:
(a) The trigger hook (a) can be kept in the released position by keeping the trigger pressed in order to allow fire.
(b) The trigger hook automatically intercepts the recoil sear and holds the recoiling mass in the cocked position, when the trigger is released or when the last round in the magazine has been fired (fig. 11). It is therefore unnecessary to recock by hand to resume firing or after changing magazines.
The recoiling mass is shown in figure 9 held in the cocked position. The barrel springs are compressed and are tending to pull the breechblock toward the muzzle (looking at fig. 9 this would be to the left). The recoil sear (d, fig. 9) is attached to the rear end of the breech bolt by an axis bolt (f).
The trigger hook (a) is hooked on the recoil sear (d), thereby preventing the breechblock and its bolt (e) from moving forward. This trigger hook (a) is pivoted on an axis bolt (g) in the trigger hook holder (h). The trigger holder (h) rests in the trigger casing (c).
Figure 9. Recoil mass being held in cocked position.
M--Parallelogram rear lever; N--parallelogram top lever; Q--parallelogram bottom lever; V--parallelogram front lever.
Figure 10. Trigger to trigger crank operation.
The trigger hook is always endeavoring to disengage from the recoil sear. This attempt to disengage is due to the action of two forces:
a. The spring (w) at the end of the trigger hook (a, fig. 9) is exerting pressure on the end of the trigger hook (a) to lift the opposite end from the recoil sear (d).
b. There is an upward thrust on the trigger hook that is caused by the forward pull of the barrel spring acting on the inclined faces of the sear and trigger hook. This is illustrated in figure 9.
Figure 11. Magazine interlock gear. Last round has been fired, trigger gear is now tripped.
NOTE.--These faces, it will be noted, do not constitute an interlocking hook, but are at such an angle that the barrel spring pull on the recoil sear tends to force the trigger hook upward and out of the engagement; simultaneously, the trigger hook spring is exerting its pressure on the trigger hook trying to disengage it from the recoil sear.
2. In the cocked position (fig. 9) upward movement of the trigger hook is blocked by the lever (m). This lever forms the rear member of a parallelogram consisting of the following:
- Parallelogram top lever (n), figure 9.
- Parallelogram front lever (v).
- Parallelogram bottom levers (q) (left and right).
- Parallelogram rear lever (m).
The four corners of the parallelogram are formed by axis pins thus allowing the four levers to pivot on each other. The pin
connecting the top and rear levers (n and m) is also mounted in the trigger casing (fig. 10).
As previously stated there is an upward thrust on the trigger hook that is caused by the forward pull of the barrel spring acting on the inclined faces of the sear and trigger. This upward thrust combined with the pressure of the spring loaded parallelogram lever plunger--rear (k, fig. 9) tends to rotate parallelogram rear lever (m) counterclockwise and thus pull the bottom levers (q)
Figure 12. Recoiling mass as to be released to fire the gun.Parallelogram being moved by trigger crank.
A--Parallelogram rear lever plunger spring; B--Trigger hook spring; FF is the poinot of contact between the parallelogram rear lever and trigger hook.
to the right. These bottom levers (q), however, cannot go to the right because they are held to the left by the breech bolt pawls (x) bearing against the lugs on the bottom levers (q). There are two levers (q) and they form the bottom levers of the parallelogram against which the right and left breech pawls (x, fig. 9) bear. These two breech pawls (x) are pivoted on the breech bolt (e). The full weight of compressed barrel springs on the breech bolt makes possible for the two levers (q) to be pulled to the right and, therefore, prevents the trigger hook from disengaging.
3. Pressing the trigger will so move the parallelogram levers (fig. 12) that the trigger hook will be released from the recoil sear and the trigger hook will be kept clear of the path of the recoiling sear as long as the trigger is pressed or until the magazine is empty. The firing is entirely automatic.
When firing, the pressing of the trigger (s, fig. 10) turns the trigger retaining bolt (z) in a counterclockwise direction. The trigger intermediate lever (aa, fig. 10) engages a pin on the trigger pawl holder and, as illustrated, this trigger pawl holder is made to turn on its axis in a clockwise rotation.
The trigger pawl holder (fig. 12) has an axis pin, and on it is placed the trigger pawl. In between the pawl holder and the pawl is a spring (ee) that is under compression in order to keep a toe on the pawl in engagement at point (y) with a notch on the trigger crank. As stated above, pressing the trigger turns the trigger bolt (z, fig. 12) counterclockwise; the trigger intermediate lever being on the same bolt is also turned counterclockwise and carries the trigger pawl with it as a unit. As stated above, the toe of the trigger is in engagement with the notch on the trigger crank, and, therefore, when the trigger pawl is rotated clockwise the trigger crank also is rotated clockwise.
At the front end of the trigger crank is another toe that lies under a lip at point (p) of the parallelogram top lever (n). Movement of the trigger crank pushes up the front end of parallelogram top lever (n) causing it to rotate about its axis pin and forcing the parallelogram to slew into the position shown in figure 12. Parallelogram bottom left and right levers (q, fig. 12) are rotated about their axis on the parallelogram rear lever (m). The front end lugs (q) of parallelogram bottom levers that were bearing against the breech pawls (fig. 12) are now disengaged. The attempt of the trigger hook to disengage itself from the recoil sear, is now about to be realized, because the levers (q) cannot restrain it, inasmuch as they are freed of the breech pawls and barrel spring. Levers (q) can now go to the right, thus forcing lever (m) counterclockwise. Springs also assist in this action as follows:
Parallelogram: rear lever plunger spring (a, fig. 14); trigger hook spring (b).--The movement of the parallelogram rear lever (m) brings it into line with a recess in the trigger hook allowing the trigger hook to rotate upward about its axis and into the
position shown in figure 13, where it is clear of the recoil sear. This disengagement from the recoil sear releases the entire breech block mass so that it counterrecoils under the push of the barrel spring, and fires the gun.
Figure13. Recoiling mass released to fire the gun.
Figure 14. Action of spring plungers against parallelogram top lever.
The trigger pawl is on an axis pin in a trigger pawl holder. In between the pawl holder and the pawl is a spring that is under, compression in order to keep a toe on the pawl in engagement at point (y) with a notch on the trigger crank. During the firing travel of the trigger pawl it remains in engagement with the trigger crank.
This action retains the trigger gear in the position shown in figure 13 as long as the trigger is kept pressed to the rear and there are cartridges in the magazine. In the position illustrated in figure 13, the lugs on the parallelogram bottom levers (q) are clear of the recoil and counterrecoil path of the breech pawls. The trigger hook is kept clear of the recoil sear by the trigger hook spring.
Releasing the trigger allows the trigger intermediate lever (aa, figure 10) trigger pawl holder, trigger pawl, and trigger
crank to return to the position shown in figure 10. The parallelogram top lever (n) is lowered by its plunger spring (fig. 14). This drops parallelogram front lever (v, fig. 13) and parallelogram bottom right and left levers (q) into such a position that the lugs on bottom levers (q) lie in the recoil and counterrecoil path of the breech pawls.
On the breech block mass recoil, the breech pawls ride under the bottom levers (q, fig. 15) and, during the subsequent counterrecoil, engage them again. The parallelogram lever (m) is still in the recess in the trigger hook as shown in fig. 15, and it is being kept in the recess by its spring. When the lugs on bottom levers (q) are engaged by the breech pawls the effect
is to pull the bottom levers (q) forward. This movement rotates the parallelogram rear lever (m) clockwise causing a face on it to press on the toe (ff, fig. 14) of the trigger hook forcing it down into engagement with the recoiling sear. The breech block mass is thus intercepted and held in the cocked position. See figure 9, "Recoiling mass in cocked position. "
Safe fire gear.--A safe fire lever is fitted close to the right handgrip. When put to the "Safe" position it turns as axis bolt and rotates the safety cam.
The toe of the safety cam contacts the rear toe of the trigger intermediate lever thus locking it and preventing any movement. When put to the "Tire" position (see fig. 10) the safety cam is rotated clear of the trigger intermediate lever.
SECTION D. MAGAZINE INTERLOCK GEAR
1. The purpose of the magazine interlock gear is to stop the gun in the cocked position after the last round of each magazine is loaded into the gun, regardless of the position of the trigger. Otherwise, the breech block mass would counterrecoil on an empty gun, making it necessary to recock by hand before firing could be continued with a fresh magazine.
2. The positions of the various parts of this gear, while the gun is firing, are shown in figure 16. The front portion of the magazine interlock gear is shown in figure 16. It should be noted that the interlock lever (d) is fastened by its axis bolt (g) to the interlock carrier (f) and the interlock rod (k) is also fastened to the interlock carrier (f) by pin (J). The interlock carrier spring (c) acts rearward on the carrier (f) when lever (d) is out of its catch recess (I). The interlock lever spring (h) acts on the lever (d) tending to keep the lever in its catch recess (i) and the front end upward.
The loading power of the magazine is by a clock spring behind the cartridge feeder in the magazine. This feeder operates against the last round in the magazine.
When the last round is fed into the gun, the cartridge feeder emerges at the mouth of the magazine (fig. 16). A bolt on the rear end of the cartridge feeder then bears down against the front end of the magazine interlock lever that is pivoted within the magazine interlock carrier and disengages it from the catch recess In the ejector. This leaves the magazine interlock carrier together
with the magazine interlock lever free to move rearward within the ejector under the influence of the interlock carrier spring. As the carrier moves to the rear, it takes with it the magazine interlock rod. The rear end of the rod pushes against the magazine interlock fork, figure 16, thus rotating the fork on its axis bolt. As the fork rotates, a part of the fork presses against a bolt that bears in turn against the claw of the trigger pawl. The movement of this bolt then trips the trigger pawl disengaging
Figure 16. Magazine interlock gear.
it from the trigger crank permitting the trigger crank to drop. This lowers the front end of the parallelogram into the position shown in figure 15. This brings the lug on the parallelogram bottom levers (q) in line with the path of travel of the breech pawls on recoil and counterrecoil. As the breech block recoils, the breech pawls slide under and past the lugs on parallelogram bottom levers (q) and on the counterrecoil engage these lugs and lock the trigger hook as shown in figure 15.
3. The action of moving the magazine catch lever toward the muzzle to free the empty magazine for unshipping (fig. 17) forces
the ejector to the rear so that it overtakes the magazine interlock carrier. This allows the magazine interlock lever, pivoted with the magazine interlock carrier, to be forced by its spring into engagement again with the recess in the ejector, thus locking the interlock carrier to the ejector once more. This movement of the ejector compresses the catch spring (fig. 17) moving the magazine catch about its pivot causing its front ends to contact the front end of the ejector thus holding the ejector in its rear position.
When shipping a new magazine a projection at the mouth presses down the forward ends of the catch (fig. 17) leaving the
Figure 17. Magazine catch lever assembly.
ejector free to move forward because of the pressure of magazine interlock catch spring (fig. 17) and lock the magazine to the gun as previously described under heading "Magazine Catch Gear and Ejector. " In the course of this action of locking the magazine when the ejector moves forward, the magazine interlock carrier is carried with it (because it is engaged in the catch recess in the ejector (fig. 17)), and the magazine interlock rod is also moved forward (because it is fastened to the carrier). This forward movement of the magazine interlock rod freezes it from the magazine interlock fork.
The magazine interlock fork and the trigger pawl tripping bolt then return to their original position (fig. 1) because of the pressure of the trigger pawl tripping bolt spring. The trigger pawl is thus left free to reengage itself with the trigger crank because of the pressure of the compressed spring between the trigger pawl holder and trigger pawl.
Note.--The magazine is held locked to the gun during the period of ejection of the cartridge. When the breech bolt mass is recoiling, the impact of the fired cartridge case against the ejector slides the ejector rearward into engagement with the recess (M) (fig. 17) of the magazine catch lever thereby preventing it from rising. Thus the magazine is held locked to the gun during the period of the ejection of the cartridge.
SECTION E. RECOILING PARTS AND BUFFERS
The chief components of the recoiling group are:
- Breech block, carrying the hammer, striker pin and breech face piece.
- Breech bolt, carrying the sear.
- Breech bars, left and right, connecting the breech block to the barrel spring case.
- Breech bolt cotter and securing bolts holding recoil parts together, as follows:
- Breech bolt cotter, holds breech block to breech bolt.
- Securing bolts and spring pins, secure barrel spring case to breech bars.
- Securing bolts and spring pins, secure breech bars to breech bolt cotter.
- Barrel spring case, mounted on the forward portion of the barrel.
- Barrel springs, mounted on the center portion of barrel, between the barrel spring case and the breech casing.
NOTE.--All the above six components move in recoil and counterrecoil.
In addition to the barrel springs, there are 2 other sets of buffer springs. A set of 12 are mounted in the front end of the gun casing, to cushion the last inch or so of recoil. A set of 15 in the
trigger casing, cushions the shock on the trigger mechanism when the trigger hook stops the gun in the cocked position.
2. The action of the striker gear is shown in figure 18 showing the striker pin being held to rear when the breech bolt is traveling forward; the hammer imparting a blow to the striker pin and the striker pin being withdrawn by the hammer.
Note.--The striker pin reaches its full firing travel by momentum and not by a direct thrust all the way by the hammer.
In order to understand the action of the hammer it should be noted in figure 18 that the front toe and rear toe are positioned out of line with each other. There are two front toes, one on each side of the hammer. The rear toe is an extension of the enter part of the hammer. The upper part of the hammer rests
Figure 18. Striker pin and hammer.
in, and operates the striker pin. The hammer plate is secured to the breech casing and has a center cam surface to operate the rear toe of the hammer and impart a thrust on the striker pin. Momentum carries the striker forward, thus firing the cartridge. (See fig. 18.)
The hammer plate has two other cam surfaces, one on each side, to operate the hammer front toes and thus withdraw the striker pin from the fired cartridge. The hammer plate cam surfaces are arranged so that the front toes are clear when the rear toe is operating, and the reverse is also true.
The three conditions of the operation of the striker gear are: (a) Breech block is traveling forward; it has picked up a cartridge, but has not quite reached the firing chamber. All three hammer toes are riding against the side of the breech casing thereby holding the striker pin to the rear. The rear toe is about to strike the rear end of the center cam surface of the hammer plate.
(b)The breech block has reached the end of its travel. The cartridge is being fired. The rear toe of the hammer is riding on the center cam surface of the hammer plate, causing the hammer to rotate forward. The hammer has driven the striker pin fully forward penetrating the primer of the, cartridge. The front toes have entered a cutaway recess in the breech casing.
Note.--The striker pin should protrude 0. 045 inch to 0. 070 inch from the breech bolt face piece when the striker pin is fully forward.
(c)The breech block has started, on recoil carrying with it the fired cartridge. The front toes have ridden up the front slope of the hammer plate causing the hammer to rotate rearward. The hammer has retracted the striker pin from the fired cartridge.
3. The breech block is connected to the breech bolt by the same cotter that connects the breech bolt to the breech bars. The purpose of breech bolt is to extend the breech block to the rear, in order to contact the trigger group. The breech bolt carries the recoil sear at the rear on an axis bolt. The right and left breech pawls are near the rear of the breech bolt. The recoil sear and breech pawls work with the trigger group as described and illustrated.
The breech block face piece is mounted in the front end of the breech block. It is retained by a shoulder that fits into a recess machined in the breech block, and is locked in place by a leaf spring. A hole is drilled in the center of the breech block face piece, to carry the rear end of the cartridge case.
4. The breech bars are connected at the rear by the breech bolt cotter that passes through the breech block and its extension, the breech bolt. The breech bars are connected at the front to trunnions forced on the barrel spring casing, The trunnions fit in holes in the breech bars. Tubular securing bolts that are secured by two-legged spring pins fasten the breech bars to the barrel spring casing trunnions at the front, and to the breech bolt cotter at the rear.
The right breech bar has a catch plate or lug for a hand cocking cable.
The right and left breech bars have hardened stop plates that contact the double-loading stop whenever a portion of a torn
cartridge case remains in the firing chamber under the double loading stop pin.
5. There are two barrel springs; a long front one in the barrel spring case and a short rear one, with a center sleeve between them. These springs are wound in opposite directions so as to prevent twist on the spring casing and on the breech bars that might be caused by twisting of a single spring. The purpose of these springs is to absorb the rearward momentum of the recoiling parts, and to return these parts to their forward position.
NOTE.--The compression on the barrel springs is 66 pounds when the recoiling parts are in their fully forward position. The compression amounts to 534 pounds when the buffer strikes the breech casing.
The casing for the barrel springs carries the recoiling end of these springs. A barrel spring front sleeve fits into the front end of the casing and is the front seat for the springs. A barrel spring center sleeve is the intermediate support for the barrel springs and is located between the two springs. It is a loose fit on the barrel. A barrel spring seating ring that is locked in the front end of the breech casing is the rear seat for the barrel springs. The recoil buffer springs, described below, assist the barrel springs.
6. A set of 12 buffer springs are mounted in the forward end of the breech casing.
These recoil buffer springs assist the barrel springs to absorb the recoil and also assist the breech block mass in counter-recoiling. They operate only during the last inch of recoil and during the first inch of counterrecoil. The total compression of the 12 buffer springs, plus the barrel springs at full metal recoil, is 3,143 lbs.
NOTE.--The gun will continue firing with recoil buffer springs broken, but it is inadvisable to allow this, except in action, as the recoil tends to become metal to metal. Parts are then liable to be damaged and the gun becomes less steady for laying and the rate of fire drops.
A recoil buffer retains the buffer springs in the breech casing, and the rear end of the barrel spring casing contacts this buffer during the last inch of recoil, compressing the springs. The
buffer is held in the breech casing by the barrel spring seating ring.
7. One of the duties of the trigger group is to intercept the recoiling mechanism, in order to keep the gun cocked whenever the trigger is released during firing, and, as the recoiling mass is moving forward at high speed, there is a severe shock at the moment of interception. The trigger buffer springs cushion this shock, thereby protecting the sear and trigger hook.
There are 15 trigger buffer springs mounted in the trigger casing.
This trigger casing also carries the trigger hook and the trigger parallelogram levers, and is locked in the breech casing by the hand grip mounting piece. The trigger casing is free to move forward a short distance by compressing the trigger buffer springs against the breech casing. This cushions the interception of the recoiling mass.
SECTION F. MAGAZINE
1. The magazine consists of a cylindrical drum containing 60 rounds of ammunition that are driven around spirals, inside the drum, by a clock spring that is hand wound from outside the magazine. The tension of the spring can be adjusted.
The feed system maintains a pressure on the innermost round, by means of a wound clock spring that is always endeavoring to push the rounds around the spirals and out of the magazine mouthpiece. The lips of the magazine mouthpiece are partly closed so that a round can pass through it only by being pushed out longitudinally at a right angle to the direction of the feed drive, a gap being cut in the front, or muzzle end, of the mouthpiece to allow the rounds to slide in or out.
2. The pressure on the innermost round is from a clock spring that is housed in the magazine casing. The outer end of the spring is held to a spring case by a securing pin. The spring case is bolted to the magazine casing by screws, thus fixing the outer end of the magazine clock spring. The inner end of the spring is hooked on the spring axis, and any tension on the spring tends to turn this spring axis. This spring axis can either rotate freely on the mainshaft, or can be coupled to it by a spring coupling sleeve having ratchet teeth. When this coupling sleeve is in
engagement the tension of the clock spring is transmitted to the mainshaft tending to rotate it.
The feed block driven by the main shaft carries the feed arm which can slide through the feed block to the radius of any point in the spiral path. The cartridge feeder link is pinned to the feed arm and to the feed head by two articulating bolts. These two articulating bolts have rollers that guide the feed system around the spiral. The cartridge feeder swivels on the feed head, pushing the cartridge around the spiral.
3. The spring axis has a spiral groove cut on its flange, and this spiral groove actuates an indicator block that slides in a radial direction. This block is an indicator of the amount of tension in the spring, and it also stops the winding or unwinding of the spring when the end of the spring axis spiral groove is reached.
NOTE.--This block does NOT indicate how many rounds of ammunition are in the magazine, but shows the amount of tension in the magazine clock spring. The zero position of the indicator block shows that it has reached the end of the spring axis groove and is holding whatever tension remains in the clock spring. In this position the ratchet teeth of the coupling sleeve can be disengaged from the main shaft thus freeing it from all spring drive.
The last round of ammunition should be fed into the magazine mouthpiece just before the indicator block reaches the end of the spring axis groove.
NOTE.--The amount of residual tension in the magazine spring is of importance as it indicates how much drive will be imparted to feeding, the last round.
4. Loading the magazine.--
NOTE.--The last two rounds loaded in each magazine should have blind loaded projectiles. This practice is generally adopted to obviate the danger of firing of an H. E. projectile through the muzzle cover.
- Place the magazine in the loading frame.
NOTE.--See if the indicator block is at zero, and if it is not, the spring tension must be relieved as instructed.
- Pull out the coupling sleeve as far as possible, and while holding it out, turn it to a point where, when released,
it is on the lugs of the main shaft and will not snap down and engage the ratchet teeth again. Turning the coupling sleeve about an eighth turn should hold it disengaged.
- Place the loading lever on the end of the main shaft. This will permit the feed axis to be revolved and thereby rotate the cartridge feeder.
- Revolve the loading lever clockwise, until the cartridge feeder is in the magazine mouth.
- Remove loading lever from coupling sleeve, leaving the coupling sleeve in its pulled out position.
- Push, by hand, through the magazine opening against the cartridge feeder, and move it back just far enough to leave space for the insertion of one or two cartridges. Never leave space for more than two cartridges.
- After a cartridge is inserted, press by hand against it, moving it back far enough to insert one or two cartridges. Continue inserting cartridges until magazine is full. Capacity of magazine is 60 cartridges.
Note.--It is essential that all cartridges be pushed all the way down to the bottom of the magazine so that their bases are in alignment and firmly seated on the magazine rear plate. This is important because the breech block moves very rapidly and the magazine must feed the cartridges to it properly, so that the face piece can readily pick up the cartridge.
CAUTION.--GREAT CARE SHOULD BE TAKEN NOT TO PUSH THE CARTRIDGES AND FEEDER A FURTHER DISTANCE THAN IS NECESSARY FOR THE INSERTION OF TWO CARTRIDGES. IF THE CARTRIDGES WITH THE CARTRIDGE FEEDER ARE PUSHED IN TOO FAR, THEY MIGHT BECOME UPSET, AND JAM. A JAMMED MAGAZINE CAN BE CAUSED BY PUSHING THE FEEDER BACK TOO FAR BY HAND, OR BY USING THE LOADING LEVER ON THE FEED AXIS. IF THIS HAPPENS IT IS NECESSARY TO DISMANTLE THE MAGAZINE TO CLEAR THE JAM.
It is sometimes impossible to push by hand a number of cartridges back into the magazine in order to make room for more, and this is particularly true toward the end of the loading
of the magazine. When this condition occurs, use the loading lever. Rotate the loading lever counter clockwise very slightly for a distance necessary for the insertion of one but NEVER OVER TWO cartridges.
CAUTION.--If the loading lever is rotated farther than this* the cartridges would have room to fall into an oblique position, thereby preventing further loading, and making it necessary to dismantle the magazine and clear the jam.
(8) When the magazine has been correctly filled to capacity (60 rounds), the coupling sleeve must be revolved by hand until it drops into engagement with the ratchet teeth.
Note.--The magazine clock spring must then be either completely, or slightly, tensioned as instructed in the following:
Completely tensioning a magazine spring.
(9) When the loaded magazine is to be used immediately, the spring is tensioned completely in the loading frame. Place the loading lever on the spring axis. Revolve the loading lever counterclockwise. Continue revolving the loading lever until a stop becomes distinctly noticeable. This indicates that the clock spring is completly tensioned. Remove the loading lever. Remove the loading magazine from the loading frame and install on a gun. DO NOT STORE A FULLY TENSIONED MAGAZINE, BECAUSE OF THE UNNECESSARY STRAIN ON THE WOUND CLOCK SPRING.
5. The indicator scale on the front cover of the magazine shows "0", "15", "30", "45", and "60" and these figures are a measure of the magazine spring tension Magazines are given either a partial spring tensioning when being stored for future use, or a complete tensioning when being used immediately. The amount of spring tensioning will depend upon how many cartridges there are in the magazine, as for example, a load of 30 or 45 cartridges requires a different spring tension than a full load of 60 rounds.
Partial tensioning of a magazine for storage purposes requires only a slight spring pressure, and the number of cartridges in the magazine makes no difference
In the case of a magazine completely filled to its capacity of 60 rounds, and fully tensioned, the indicator will read "60".
In case the magazine has a partial load of cartridges, then the spring is tensioned according to the load in the following manner: There are openings in the hack plate of the magazine through which the rear ends of the cartridges are visible. Tension the spring for 10 more cartridges than there are in the magazine
Note.--Hold the coupling sleeve with the fingers to prevent its turning when tensioning the spring on a partly loaded magazine. If it is permitted to turn, the cartridge feeder will be backed away from the cartridges and a jam may result.
(a) When a fully or partly filled magazine is to be stored, the spring is given a slight initial tensioning that is just sufficient to hold the cartridge upright.
Note.--A short tensioning with the loading lever in the position is sufficient. If the magazine is fully loaded or only partly filled, this slight initial tensioning is necessary to prevent a jam in the magazine.
(b) If no initial tensioning is given the magazine spring, the cartridges are liable to fall out, become disarranged, or Be tipped over when the magazine is lifted from the loading frame.
It may become necessary to relieve the spring tension on the magazine feed block to unload, to store, or to strip the magazine.
6. (a) Place the magazine in the loading frame in the same manner as when loading. Place loading lever in the spring tensioning axis.
NOTE.--The loading lever will not clear the magazine handle, so place it in such a position that it has room to move clockwise from one side of the handle to the other.
(b) The tension of the spring causes pressure on the ratchet teeth of coupling sleeve. Therefore, press counterclockwise on the loading lever to relieve this pressure and at the same time disengage the coupling sleeve with the other hand by pulling outward and turning about one-eighth turn, so that the sleeve stays disengaged.
(c) Allow the loading lever to move clockwise, as far as it can (until it contacts the magazine handle). Turn the coupling
sleeve slightly and allow it to snap down and mesh the ratchet teeth.
(d) Press on the loading lever ratchet pawl and revolve the loading lever back to position from which it started in step 1. Then release the pawl.
(e) Repeat step c. until the spring tension is completely relieved and no pressure can be felt against the lever.
Note.--If the cartridges are to be left in the magazine, the spring must be given a slight initial tension before taking the magazine out of the loading frame in order to prevent their falling out or being tipped over.
7. If a magazine is loaded with cartridges and has been fully spring tensioned, and it is desired to unload the cartridges and relieve the tension of the magazine clock spring, this can be done by pushing the cartridges out, one hj one. This action removes the cartridges and relieves the spring tension at the same time. It is not necessary to use the loading lever or disconnect the coupling sleeve.
8. It is advisable to relieve the initial spring tension completely and this is done by using Steps a, b, c, and d, these being the same as for "Relieving Magazine Spring Tension". In this case of initial tensioning, the loading lever will relieve the slight initial tensioning in the first four steps, and the fifth step will be unnecessary. Place the loading lever so that it is all the way down and revolve it clockwise with one hand, so that a cartridge is constantly being pressed against the magazine mouthpiece. Use the other hand, and push out the cartridges as they appear at the mouthpiece.
NOTE.--The loading lever must be made to revolve continuously as the cartridges are being removed, or the cartridges will upset and jam. IF THIS HAPPENS IT IS NECESSARY TO DISMANTLE THE MAGAZINE TO CLEAR THE JAM.
9. It is advisable to relieve the spring tension by using steps (a), (b), (c), (d), and (e), paragraph 6 above, and then unload the cartridges as instructed above.
NOTE.--The magazine should be stripped by an artificer.
- Place the magazine in loading frame.
- Empty the magazine of cartridges unless the stripping is being done to eliminate a jam, in which case it will be
necessary to proceed with cartridges still in the magazine.
- There are eight screws that hold the cover plate on the magazine. Remove six of these, leaving in place any two that are directly opposite each other.
- Install the loading lever on the spring axis and relieve spring tension pressure as instructed.
- With coupling sleeve disengaged, place the loading lever on the feed axis, and revolve it counterclockwise, until the cartridge feeder is at the inner end of its travel.
- Turn the coupling sleeve so that it snaps down and engages the ratchet teeth.
- Install the loading lever on the magazine spring axis and turn the loading lever counterclockwise just far enough to take the slight remaining spring tension.
- Hold the loading lever in the position described in step 7, and remove the two remaining screws from the cover plate. Keep the loading lever in the position given in Step 7, and loosen the cover plate from the magazine with a screw driver or suitable tool, being very careful not to pry up the spring casing flange.
Note. ---The loosening of the cover plate with a screw driver frees it from the spring casing, and now the remaining spring tension may be allowed to rotate the loading lever clockwise.
- All spring tension is now eased off and the loading lever can be unshipped.
- Rotate the spring housing assembly until one of the holes in the coupling sleeve is in line with the head of ratchet cross pin.
- Lift the spring case until its flange clears the dowel screw in the front plate, and turn it until the letters "D" in the front plate and cover plate are in line. Remove the spring case completely with the spring axis. The spring can be removed from the casing by pushing the spring up on the bolt and holding it to the casing. This will permit the enlarged part of the hole to be lifted over the bolt. The spring can then be removed from the spring axis by twisting the axis so as to disengage the lugs from the holes in the inner end of the spring.
- Remove the snap ring from the rear end of the main shaft, using pliers.
- Remove the complete main shaft, feed block, feeder link and cartridge feeder from the front.
- The feeder link, feed block, and cartridge feeder can be separated by removing the bolt cotter pins and tapping out the two articulating bolts, and feeder swivel bolt, using punch.
- The magazine casing should not normally be stripped into its component parts.
10. Thoroughly lubricate all parts.--See Magazine Maintenance.
- Assemble the main shaft, feed block, feeder arm, feeder link, two articulating bolts with their rollers, feed head, bolt washers, bolt cotter pins and cartridge feeder.
- Lubricate, and insert this feed group assembly into the magazine from the front. Engage the rollers in the spiral guideway. Insert the rear end of the main shaft into its bearing in the rear plate.
- Assemble the snap ring at the rear end of the main shaft. To check the action, turn the feed system so that the cartridge feeder is outward at the limit of its travel in the empty position.
- Place the enlarged part of the hole in the magazine spring over the bolt in the spring casing, and pull the spring down onto the bolt shoulder and out of the enlarged part of the hole. Pack the magazine spring with Gulf Plastic AS Special grease. Insert the magazine spring in its case over the spring axis, and turn the axis so as to engage the axis lugs. Insert this assembly into the magazine with the letters "D" in line. Rotate the spring case until the dowel hole marked "O" in its flange engages the dowel screw in the front plate of the magazine.
Note.--Examine the spring case holes that are counterclockwise from the hole marked "O. " In a few cases they may be marked "1," "2," "3," and up. If these markings are found, then turn the spring case so that the hole with the highest number, instead of the hole marked "O," is
engaged with the dowel screw on the front plate of the magazine.
- Place the cover plate on the magazine, and do not install any screws in it. Move the indicator block with a knife blade, or any similar tool, so that it engages in the spiral groove on the spring axis.
NOTE.--Up to this point it is permissible to have the cover plate in any position; also the indicator block can be engaged in the spiral groove of the spring axis in any position.
- Turn the cover plate counterclockwise until the indicator shows zero and the indicator block can be felt coming up against the clock spring.
- Assemble the coupling sleeve with its spring, the retaining ring and the cross pin.
- Ship the loading lever on the spring axis and turn the loading lever counterclockwise about seven-eighths of a revolution or until the letter "A," stamped on the cover, is in alignment with letter "A" stamped on the magazine casing.
- Maintain this position by holding the loading lever, and install eight cover screws.
CAUTION.--The counterclockwise rotation of the cover from the zero position in Step 6 to "A" alignment in Step 8, has to be done against the clockwise pull of the clock spring. Approximately seven-eighths' revolution of the cover by loading lever should bring the alignment marks "A" opposite each other. BE VERY CAREFUL NOT TO TURN MORE THAN THIS AMOUNT. ALSO, DO NOT ALINE MARKS "A" BY TURNING THE LOADING LEVER CLOCKWISE.
11. If a magazine becomes dry or corroded internally, it must be disassembled, cleaned, and lubricated with Gulf Plastic AX special grease. See instructions for disassembling and reassembling magazine.
12. The magazine clock spring was packed with grease, when the magazine was issued. However, this grease tends to squeeze out in service. Watch this spring for evidences of corrosion,
and if corrosion is found, disassemble, clean and repack with Gulf Plastic AX special grease.
13. The spring that is behind the magazine interlock bolt may become corroded, or operate slowly, due to the use of too thick an oil, or because the oil thickened in cold weather. This magazine interlock bolt is the part on the magazine cartridge feeder that causes the gun to be held in a cocked position when the magazine has fed its last round to the gun. Therefore, any corrosion or slow operation due to thick or thickened oil will cause the gun to fail to remain in a cocked position after firing the last round of each magazine. Use Gulf Plastic AX special grease, or ice machine oil, and apply sparingly and often.
14. All moving parts should be lightly coated with Gulf Plastic AX special grease. A light coat of the same grease should be applied to the spiral guideways in the magazine.
SECTION G. GUN MAINTENANCE
1. The cleaning and oiling of the gun should be carried out as required and not at any fixed intervals.
It should be realized that in this type of gun the force of explosion is absorbed in checking and reversing the forward movement of a relatively heavy bolt that is never locked. The proper functioning of the gun depends on the free movement of the recoiling parts and on the free operation of the various springs used.
Any dirt, corrosion, or lack of lubrication that is present to a degree that will impede free movement and free operation will cause stoppages during firing.
2. Clean and Oil--
- As soon as possible after firing.
- If the gun gets wet.
- If the gun gets dirty.
- If there is any reason to expect corrosion to start.
In order to clean and oil the gun properly it is necessary to first partly disassemble it.
3. Use mineral oil or any good quality lubricating oil of medium viscosity. CAUTION.--Do not add white lead, black lead, red lead, or make any addition of any similar substance to the oil.
4. The double loading stop plunger, upper, and the double loading stop plunger, lower, in the barrel tend to become stuck with oil that is gummed by the heat of the gun. These parts should be cleaned periodically and lubricated with a light viscosity oil, applied sparingly and often.
To remove the double loading stop plunger, lower, from the barrel, take out the retaining pin using the special screw driver. The plunger can then be taken out for cleaning and lubrication.
CAUTION.--If the parts of the double loading stop gear become gummed or corroded, the stop plunger, lower, might not be operated, resulting in stoppage.
5. The parts of the double loading stop gear and also the buffer are exposed to salt-water corrosion and, therefore, require particular care in maintenance. See "Caution" note above.
6. When the gun is being mounted in the cradle, the inside of the securing bolt hole, the breech casing, and the securing bolt itself, should be thoroughly greased for protection against corrosion.
7. If the gun stops of its own accord, for any reason other than an empty magazine, the following immediate action should be carried out:
(a) Put the safety catch to "Safe" and note whether the recoiling parts are in the forward position. If the recoiling parts are in the forward position, a misfire, a broken striker, a broken hammer, or failure to feed from the magazine, is indicated. Safety precautions for a misfire should be observed.
If there is a live round in a hot gun and the stoppage cannot be cleared then douse the barrel with water, to prevent the round from heating up.
If the magazine is empty and the gun stops in the forward position, it may be due to sticking, or sluggish action of the magazine cartridge feeder bolt which trips the interlock lever. If examination shows that this bolt does not work freely, the magazine should not be used again until the condition has been corrected.
(b) Examine the double loading stop. If the horns are in the down or operating position, there is a round or part of a broken case in the chamber.
(c) Remove the magazine and recock the gun. If the magazine is difficult to remove, it will come off as the breech block
is withdrawn when cocking the gun. In the event of it being impossible to remove the magazine without recocking, care should be taken to cock the gun in one continuous movement, and on no account must the breech block be allowed to go forward.
(d) Examine chamber and breech face piece. If the lip of the breech face piece is broken off, a new one must be installed.
(e) Examine the bore from the muzzle, making sure it is clear. This is necessary to avoid a premature or bulged barrel. An ejector tool is provided in the tool roll, to remove any HE shell or practice shell left in the bore. This ejector should be used gently, and, if excessive resistance is felt when removing an HE shell, then change the barrel.
(f) Stoppages of the gun have occurred which appeared to have been caused by the presence of hair from ammunition packing material getting into the mechanism. Steps have been taken to eliminate this type of packing, but a large amount of ammunition has already been issued. At the first opportunity, and in any event before loading it into the magazine drums, ammunition should be examined to see that it is free of hair; and if hair or dirt is found, it should be removed. If grease is removed in this process, it must be replaced.
8. The outside of the barrel, and the outer and inner surfaces of the barrel springs, should be smeared with dry graphite or grate polish.
NOTE.--Oil should not be used on the outside of the barrel nor on the barrel springs as it smokes when the barrel gets hot, and the smoke will interfere with the sighting of the gun.
9. The bore and firing chamber should be lightly cleaned out IMMEDIATELY AFTER FIRING using the cleaning rod equipment in the tool roll.
Place a light coat of a good quality lubricating oil, medium viscosity, in the bore and firing chamber.
CAUTION.--Do not fire with a heavily greased bore or firing chamber.
The proper functioning of the gun requires easy and regular extraction of the empty cartridge case, when it is blown backward by the firing chamber gases. Care must be taken, therefore, to maintain the firing-chamber walls in good condition, thereby avoiding any unnecessary friction with the walls of the
cartridge case. The firing-chamber walls have a high lapped polish when the barrel is issued. FIRING-CHAMBER WALLS MUST NEVER BE CLEANED WITH EMERY PAPER.
10. The amount of life that a barrel will give, depends on how hot the barrel becomes during firing.
Five magazines, containing 60 rounds each or a total of 300 rounds, can be fired continuously without harm to the barrel.
Nine magazines of 60 rounds each, or a total of 540 rounds, will cause serious wear if fired continuously.
If short pauses occur between the firing of each magazine, the wear will remain small, even after several thousand rounds.
During any prolonged firing, keep the barrel as cool as possible, either by frequent changes with the spare barrel, or by dousing the barrel with water.
11. The barrel is removed by rotating the barrel locking handle into the position marked "unlock. " Rotate the barrel approximately 60° counterclockwise looking from the muzzle to the breech and pull out to the front (asbestos gloves are provided with the tools and spare parts to remove a hot barrel) .
Note.--The clearances between the barrel and its housing in the breech casing are very small. Therefore, a barrel may fit very tightly and a special tool is provided for rotating the barrel.
12. The barrel can be removed easily and quickly and another barrel substituted without disassembly of any other parts.
Interrupted thrust collars, machined on the barrel, secure it to the casing. The barrel is assembled from the front with its interrupted thrust collars in the unlocked position. The barrel is then locked by rotating it 60° clockwise looking from the muzzle toward the breech. Assembly marks are provided. The barrel is prevented from accidental unlocking by the barrel locking gear as already described.
The barrel, when rotated into its position, is stopped by a pin mounted in the breech casing that fits into a slot in the rear end of the barrel. This locates the barrel in the proper position to engage the barrel locking lever. The double loading stop prevents loading a round of ammunition into the barrel chamber unless the chamber is already clear at the double loading stop. A hole is drilled through the top wall of the chamber of the barrel and in this hole the double loading stop plunger operates. The operation of the double loading stop has already been described.
13. If violent recoils, causing metal to metal contact of the buffer against the breech casing, occur habitually, and more than one lot of ammunition has been used during these metal to metal recoils, then the cause is probably a collapse of the barrel springs and not a result of ammunition loading.
A metal-to-metal contact always occurs between the barrel spring casing and the buffer during the last inch of recoil. However, the buffer should not normally strike the breach casing. Weak barrel springs will cause the buffer springs to be overloaded and result in metal-to-metal contact of the buffer against the breach casing.
The remedy is to change to the spare barrel springs. H spare barrel springs are not available then insert flat washers at the rear end of the barrel spring up to a maximum thickness of three-fourths of an inch.
CAUTION.--Whenever possible keep the gun UNCOCKED in order to relieve the spring tension and prevent the possibility of a permanent set of the springs.
14. If the buffer becomes corroded it may not have the free movement necessary to transmit the last of the recoil shock to the buffer springs, and the free movement necessary to assist the barrel springs on counterrecoil.
15. The ratchet type hand cocking tool supplied with some of the Mark 2 guns is principally for use when the gun is dismounted from its carriage. This hand-cocking tool can also be used on the Mark 4 gun.
16. To use the hand-cocking tool, first remove the shoulder piece from the breech casing and install the hand-cocking tool in its place on the threads of the breech casing. Hook the end of the chain on the cocking catch plate on the rear end of the right breech bar.
17. Pull the breech block mass back by using the hand-cocking tool handle. The breech pawls can be heard to, click over the parallelogram bottom levers when the breech block mass has been pulled far enough to the rear. The hand-cocking tool handle can then be eased back until the sear engages the trigger hook by following the instructions under "Uncocking with the ratchet type hand-cocking tool."
18. Three other types of hand-cocking devices will be found in use with various guns.
(1) Double lanyard.--A stirrup which slips over the barrel and comes up against the barrel spring casing has a lanyard attached to each side. These lanyards are knotted to provide hand holds. The gun can be cocked by having two or three men pull on each lanyard.
(2) Single lanyard.--Another device is a single lanyard with a ring on one end and several knots to provide hand holds. The ring is slipped over the left end of the cotter and the gun is cocked by the pull of four or five men on the lanyard.
(3) Block and tackle.--A block and tackle type cocking device is used by hooking the front end in one of the holes in the left breech bar. The rear end is shipped over the hand grip and the gun cocked by the use of the block and tackle.
NOTE.--Normal cocking is done most quickly with the single or double lanyard device. To clear a jammed cartridge from the chamber may require considerable force. For this purpose use the ratchet type tool, the block and tackle, or the mount cocking rope.
19. The hand cocking tool supplied with some Mark 2 guns can be used to uncock the gun by removing the shoulder piece from the breech casing and installing the hand cocking tool in its place on the threads of the breech casing. Hook the end of the chain on the cocking catch plate on the rear end of the right breech bar.
DO NOT SLAM THE BREECH MASS ON AN EMPTY GUN. Ratchet the hand cocking tool lever so as to make the chain taut enough to hold the breech mass from slamming. Remove the magazine by pressing the magazine catch lever forward while lifting the rear end of the magazine clear of its catch and the ejector. Press down with any suitable tool on the end of the magazine interlock lever, in order to release the interlock. Press the trigger and the breech mass will be held from running forward by the hand cocking tool.
Pull on the handle to relieve pressure on the holding pawl. Release holding pawl by pressing forward on the holding pawl lever. While holding lever allow handle to rotate forward a convenient distance. Remove finger pressure from holding pawl lever. Apply finger pressure to handle pawl and revolve the
handle back to its starting position. Then release the pawl. Continue to repeat the above procedure until the breech mass has been eased forward.
The other types of cocking devices described previously can be used to prevent the breech mass from slamming on an empty gun.
20. The normal method used during firing or drill for cocking a gun that is assembled on the mount is to use the mount cocking rope.
Rotate the handwheel so as to lower the gun and its carriage to their lowest position. Elevate and lock the gun at 87°.
Attach one end of the wire cocking rope on the breech cotter. Attach the other end of the cocking rope to the mount cocking bracket.
Turn the gun and its carriage so that the cocking rope is in a direct line to the left side of the gun.
Rotate the handwheel so as to raise the gun and carriage. The downward pull of the cocking rope on the breech block mass will cock the gun.
The breech pawls can be heard to click over the parallelogram bottom levers when the breech block mass has been pulled sufficiently to the rear. The breech block mass can be eased forward by lowering the gun and carriage with the handwheel until the sear is engaged by the trigger hook.
21. Do not slam the breech mass on an empty gun. Rotate the handwheel so that the gun and carriage are at their lowest position. Elevate and lock the gun at 87°. Attach one end of the cocking wire rope to the breech block cotter, and the other end to the mount cocking bracket. Turn the gun on its carriage pivot so that the cocking rope is in a direct lead to the left side of the gun. Rotate the handwheel to raise the gun upward from the mount so that the cocking wire rope is taut enough to hold the breech mass from slamming. Remove the magazine clear of its catch and the ejector. Press down with any suitable tool on the end of the magazine interlock lever in order to release the interlock. Press the trigger, thereby releasing the recoiling mass. The cocking rope will then hold it from running forward. Ease the recoiling mass forward by lowering the carriage by turning the handwheel.
SECTION H. PARTIAL STRIPPING
1. DO NOT SLAM THE BREECH MASS ON AN EMPTY GUN. Rotate the handwheel so that the gun and carriage are at their lowest position. Elevate and lock the gun at 87°. Attach one end of the cocking wire rope to the breechblock cotter, and the other end to the mount cocking bracket. Turn the gun on its carriage pivot so that the cocking rope is in a direct line to the left side of the gun. Rotate the handwheel to raise the gun upward from the mount so that the cocking wire rope is taut enough to hold the breech mass from slamming. Remove the magazine by pressing the catch lever forward while lifting the rear end of the magazine clear of its catch and the ejector. Press down with any suitable tool on the end of the magazine interlock lever in order to release the interlock. Press the trigger, thereby releasing the recoiling mass. The cocking rope will hold it from running forward. Turning the handwheel in the direction to lower the carriage will ease the breech mass forward.
2. Remove the four breech bar securing spring pins. Remove the four securing bolts securing the breech bars to the cotter and to the barrel spring casing. Take the pull of the barrel springs off the breech bolt cotter by having a second man push the barrel spring casing slightly toward the rear. Slide the cotter out to the left. Instruct the second man to release the barrel spring casing. Remove the breech bars by disengaging them sideways and slide the barrel spring casing clear over the muzzle. Also slide the barrel springs and the guide sleeves clear over the muzzle.
3. Press the catch that retains the handgrips and remove the handgrips by unscrewing counterclockwise.
4. Slide the trigger cover plate off to the rear. Pull out the trigger casing to the rear, complete with the trigger gear and trigger buffer springs. Remove the trigger buffer springs. Remove the trigger snap ring using the special pliers in tool roll. Pull the assembled trigger hook holder out to the rear. The trigger hook on its axis bolt and its spring will be pulled out with the trigger hook holder.
NOTE.--A strong pull is required. Drive out the trigger hook axis bolt and lift out the trigger hook and its spring.
5. Slide the breechblock and the breech bolt out the rear of the breech casing. Remove the recoil sear axis bolt snap ring with the special pliers in the tool roll. Drive out the recoil sear axis bolt and lift out the sear and its spring.
6. Insert a punch (from tool roll) in the recess under the lip of facepiece securing spring and bend the spring clear of the face-piece. Turn the facepiece 90°, either way, with facepiece spanner tool and pull the facepiece out.
7. Remove the hammer axis bolt by turning it 180° and pushing it out. The hammer is free and can be lifted out. The striker pin will then drop to the rear, out of the breech block.
8. Rotate the barrel locking handle into the position marked "Unlock. " Rotate the barrel counterclockwise, looking from the muzzle to the breech, until stopped by the stop pin (approximately 60°) and pull out to the front.
NOTE.--The clearances between the barrel and its housing in the breech casing have to be very small and consequently the barrel may feel tight. A special tool is provided for rotating the barrel. Asbestos gloves are provided for the handling of hot barrels.
9. Remove the retaining pin, using the special screw driver from the tool roll. The double loading stop plunger can then be taken out.
10. Drive out the barrel locking handle pin, using tool. Drive out the barrel locking lever axis bolt from the left to the right, using special punch in tool roll. This will free the barrel locking handle for removal. Lift out the double loading stop, together with its two plungers and two springs. Lift out the barrel locking lever. Lift out the barrel locking lever plunger and its spring. Remove the double loading stop axis bolt securing spring with special pliers in the tool roll. Tap out double loading stop lever and its plunger and its spring. Bend down the upturned lug on the double loading stop guide bushing locking washer. Unscrew the double loading stop guide bushing with spanner in tool roll. This will carry the double loading stop plunger (upper) along with it. Lift out the locking washer.
11. Press in on the barrel spring seating ring retaining catch. Unscrew and remove the barrel spring seating ring, using spanner in tool roll.
NOTE.--The barrel spring seating ring has a right-hand thread. Pull the buffer out to the front. Remove the 12 buffer springs.
12. Rotate the magazine catch lever toward the muzzle so as to engage the catch. Press in the axis bolt securing spring and drive out the axis bolt. Remove the magazine catch lever. Release the magazine interlock catch by pressing down with a suitable tool on the front ends of the catch. This releases the ejector. Slide out to the front the ejector complete with the magazine interlock rod, interlock lever, interlock carrier, interlock lever spring, interlock carrier pin, and interlock carrier axis.
Inspection and Adjustment After Partial Stripping
This completes partial stripping and next steps are:
- Clean and oil the gun as instructed.
- Inspect and adjust as follows:
The gun should be carefully examined, after partial stripping, for cracks in:
- Buffer springs.
- Lip of the breechblock facepiece.
- Striker pin.
- Trigger hook.
There is a tendency for the striker pin to "set up" after long use.
See that the striker pin works freely in the breechblock.
Examine all springs. Spares are supplied in the spare parts box for every spring.
The limits for protrusion, in service, are between 0. 045 inch and 0. 070 inch. This measurement is to be made with the striker pin pushed fully forward in the bolt.
NOTE.--If the protrusion is too high, the point of the striker should be dressed back. If the protrusion is too low, there in no adjustment, and a spare striker pin should be shipped.
CAUTION.--Make certain that the striker pinhole in the breechblock is free of burrs, dirt and corrosion.
As previously stated, the striker pin reaches its full firing travel by momentum and not by a direct thrust all the way by
the hammer; therefore, wear of the hammer and hammer plate is not important.
1. Assemble the interlock rod and the interlock lever together with its spring to the carrier. Insert one of the springs into the interlock carrier. Slide the interlock carrier, complete with the interlock rod (as assembled above) into the ejector from the rear and push forward against the spring until the carrier is held by the lever springing into the catch recess in the ejector. Insert the magazine interlock catch into its recess in the breech casing. Insert the two remaining springs and slide the ejector (as assembled above) into the breech casing from the front, taking care that the rod passes through its guide block. Hook the front toe of the magazine catch lever into its recess in the ejector. Pull the lever and the ejector bodily backwards against the springs until the rear toe of the lever can be hooked behind the catch and thereby hold the ejector temporarily in position. Then insert the magazine catch lever axis assembly through the lever.
2. Install double loading stop guide bushing locking washer. Install double loading stop guide bushing using spanner in the tool roll. Install double loading stop plunger upper. Install double loading stop spring case and its spring for the double loading stop lever. Install barrel locking lever plunger and its spring. Install double loading stop lever, install its axis bolt, tapping it from right to left; install its securing spring using special pliers in the toll roll. Install barrel locking lever. Install double loading stop together with its two plungers and two springs.
NOTE.--To accomplish this, first insert the two sets of springs and plungers into the stop. Face toward the muzzle and hold these in place with the first fingers of each hand. Then insert the stop without letting the plungers come out. Install the barrel locking handle. Install the barrel locking handle pin.
3. Install the 12 buffer springs in the breech casing. Install the buffer from the front. Screw in the barrel spring seating ring using spanner from tool roll.
NOTE.--The barrel spring seating ring has a right-hand thread.
CAUTION.--Hold the barrel spring seating ring retaining catch inward while tightening this seating ring.
4. Insert the double loading stop plunger lower in its hole in the barrel. Lock this in place inserting the retaining pin and, tightening securely with the special screw driver. Check to be certain the double loading stop plunger operates freely in the barrel. Place the barrel locking handle into the position marked "Unlock. "
Insert the barrel with the "Insert" arrow in line with the arrow on the breech casing.
When inserting the barrel, press down the horns of the double loading stop. This will prevent the double loading stop plunger in the breech casing from scoring the surface of the barrel.
Note.--Push completely in.
Rotate the barrel clockwise, looking from the muzzle, until it is stopped by the barrel stop pin (approximately 60°) . Place the barrel locking handle in the "Locked" position; then make certain that the barrel is locked against rotation by trying to turn it counterclockwise, looking from the muzzle.
5. Insert the striker pin. Push it into the forward position and see that its slot is in line to receive the top portion of the hammer. Insert the hammer into the slot in the striker pin. Insert the hammer axis bolt in the hole in the hammer nearest the toes. Lock the axis bolt by rotating it 180° so that it lies flush with the surface of the breech block.
6. Place the sear spring and sear in position on the breech bolt and install the sear axis bolt. Install the sear axis bolt snap ring using the pliers in tool roll. Install the breach bolt as assembled above in the breech block. Slide the two together into the breech casing and push into the forward position.
7. Place the trigger hook and trigger hook spring in position in the trigger hook holder. Install trigger hook axis bolt. Install the assembled trigger hook and holder from the rear into the trigger casing.
NOTE.--A strong push is necessary when inserting the trigger hook into the trigger casing.
Install the trigger snap ring using the special pliers in tool roll. Install the trigger buffer springs. Slide the trigger casing assembly
into the breech casing from the rear. Slide the trigger cover plate, on, from the rear.
8. Screw on the handgrips. They should stop with the engraved number UP and with the handgrip catch engaged to prevent rotation.
NOTE.--AT THIS POINT OF REASSEMBLY TEST THE OPERATION. Test the trigger gear, breechblock, and breech bolt for correct action by bringing the breechblock and bolt, with the cotter in place, to the rear and then pushing them forward again until they are held by the trigger gear. Trip the magazine interlock gear, press the trigger and see that the block and bolt are thereby fully released.
9. Install the short barrel spring to the rear. The smaller-diameter end of the spring goes to the rear. Install the barrel spring center sleeve. Install the long barrel spring. Install the barrel spring front sleeve. Larger outside diameter end of this sleeve goes toward the front. Slide the barrel spring casing on, with the engraved number UP. Place the breech bar securing bolts. Have a second man take the pull of the barrel springs by pushing on the barrel spring casing toward the rear. While holding the pull of the barrel springs, insert the breech cotter from left to right and pass it through the left-side breech bar, breechblock, breech bolt, and right-side breech bar. Instruct the second man to release the barrel spring casing. Assemble the four breech bar securing bolts and their four spring pins. This connects the breech bars to the barrel spring casing and to the breech cotter.
NOTE.--The flanged ends of the securing bolts should be UP and the two tongues of the spring pins should be left athwart the gun. If left fore and aft, they will have a tendency to become disengaged on firing.
SECTION I. CARE OF THE GUN
1. If the gun is left in the secured position it should be uncocked in order to relieve the stress on the barrel springs.
The magazine catch has to be tripped in order to uncock the gun and should be left in that state in order to ease the springs in the ejector.
2. The muzzle cover should be placed over the end of the barrel.
NOTE.--An HE shell should not be fired through a muzzle cover. The last two rounds loaded in each magazine should have blind loaded projectiles.
3. DO NOT SLAM THE BREECH MASS ON AN EMPTY GUN. Rotate the handwheel so that the gun and carriage are at their lowest position. Elevate and lock the gun at 87°. Attach one end of the cocking wire rope to the breech block cotter and the other end to the mount cocking bracket. Turn the gun on its carriage pivot so that the cocking rope is in a direct line to the left side of the gun. Rotate the handwheel to raise the gun upward from the mount so that the cocking wire rope is taut enough to hold the breech mass from slamming. Remove the magazine by pressing the catch lever forward while lifting the rear end of the magazine clear of its catch and the ejecter. Press down with any suitable tool on the end of the magazine interlock catch in order to release the interlock. Press the trigger, thereby releasing the recoiling mass. The cocking rope will then hold it from running forward. Turning the handwheel in the direction to lower the carriage will ease the breech mass forward.
The use of the different hand methods for uncocking are given in section G, par. 18.
4. All 20-mm. antiaircraft ammunition MUST BE COMPLETELY COVERED WITH A LIGHT COAT OP A SUITABLE GREASE BEFORE BEING LOADED INTO THE MAGAZINE.
As previously stated, the ammunition is packed greased; however, this grease tends to dry off and must be regreased before being loaded into the magazine.
Note. -A small amount of a suitable grease applied, shortly before firing, to the cartridge case that is . visible in the magazine mouthpiece will assist in preventing a jam in the gun barrel.
Dry ammunition or ammunition with insufficient grease will jam in the gun chamber when fired and extraction will be very difficult, if not impossible.
NOTE.--Oil must not be used as a substitute for miners 1 grease.
Sufficient grease should be present on all cartridge cases to be easily felt by the fingers but an excess should be avoided, Caution.--Do not grease the rear end of the cartridge cases as the grease has a tendency to percolate inward, past the percussion cap. NEVER USE OIL.
5. If the gun stops of its own accord, for any reason other than an empty magazine, the following immediate action should be carried out:
(a) Put the safety catch to "Safe" and note whether the recoiling parts are in the forward position. If the recoiling parts are in the forward position, a misfire, a broken striker, a broken hammer, or failure to feed from the magazine is indicated. Safety precautions for a misfire should be observed. If there is a live round in a hot gun and the stoppage cannot be cleared, then douse the barrel with water to prevent the round from heating up. If the magazine is empty and the gun stops in the forward position, it may be due to sticking, or sluggish action of the magazine cartridge feeder bolt which trips the interlock lever. If examination shows that this bolt does not work freely, the magazine should not be used again until the condition has been corrected.
(b) Examine the double loading stop. If the horns are in the down or operating position, there is a round or part of a broken case in the chamber.
(c) Remove the magazine and recock the gun. If the magazine is difficult to remove, it will come off as the breech block is withdrawn when cocking the gun. In the event of it being impossible to remove the magazine without recocking, care should be taken to cock the gun in one continuous movement, and on no account must the breech block be allowed to go forward.
(d) Examine chamber and the breech facepiece. If the lip of the breech facepiece is broken off, a new one must be installed. (e) Examine the bore from the muzzle, making sure it is clear. This is necessary to avoid a premature explosion or bulged barrel. An ejector tool is provided in the tool roll, to remove any HE shell or practice shell left in the bore. This ejector should be used gently, and if excessive resistance is felt when removing an HE shell, then change the barrel.
(f) Stoppages of the gun have occurred which appeared to have been caused by the presence of hair from ammunition packing
material getting into the mechanism. Steps have been taken to eliminate this type of packing, but a large amount of ammunition has already been issued. At the first opportunity, and in any event before loading it into the magazine drums, ammunition should be examined to see that it is free of hair; and if hair or dirt is found, it should be removed. If grease is removed in this process, it must be replaced.
SECTION J. 20 MM. GUN COMPLETE STRIPPING AND ASSEMBLY
1. The stripping operations listed under "Partial stripping" are sufficient for normal inspection and cleaning.
In case of damage to, or failure of, the smaller parts, further stripping may be necessary.
A number of these operations are independent of any other and care should be taken not to disassemble further than necessary, as for instance:
Example.--The barrel is not the first operation on the list for partial stripping, yet it may be removed normally without taking off any other part.
The complete stripping instructions given below are a continuation of the partial stripping.
(a) Under partial stripping the following were removed:
Trigger cover plate.
Trigger hook and holder.
Trigger casing complete.
Trigger buffer spring.
Drive out the parallelogram lever axis bolt-rear top in either direction. Remove the trigger parallelogram complete. Remove the parallelogram spring box by driving out its axis bolt in either direction. A special punch is in tool roll.
(b) Remove the two retaining pins from the parallelogram lever axis bolt-bottom, front.
Remove the spacing sleeve pin, and lever axis bolt, top front sleeve. Drive out the parallelogram lever axis bolt-top front. Drive out the parallelogram lever axis bolt-bottom front.
NOTE.--Special punches are in the tool roll.
(c) Drive out the two vertical pins that are used to secure the two outer plungers.
Remove the horizontal pin that is used to secure the central plunger.
NOTE.--There are two parallelogram lever plungers, front, and there is one parallelogram lever plunger, rear, that can be pulled out with their two springs and one spring.
(d) Drive out the trigger pin in the hub of the trigger using special punch in tool roll. Tap out the trigger retaining bolt inward using special punch in tool roll. Lift out the trigger. Tap out the trigger crank inward using special punch in tool roll. Lift out the trigger pawl and the pawl holder together. Note.--The pawl can be separated from the pawl holder by-driving out the pawl axis pin from left to right. Lift out the trigger intermediate lever.
(e) Drive out, from left to right, the safety gear axis bolt pin. This pin secures the safe/fire lever to the axis bolt. Drive out the safety gear axis bolt.
NOTE.--This frees the safe/fire lever and the safety cam. (f) Follow operation 5, of "Partial stripping," necessary for examination of the sear for fractures. Remove the "magazine interlock lever from the carrier by driving out its axis bolt. Note.--This also releases the magazine interlock lever spring. I Lift out the interlock catch. Remove the magazine interlock fork by driving out its axis bolt in either direction.
(g) Drive out the trigger pawl tripping bolt spring case retaining pin. This pin secures the spring case to the breech casing. Remove the spring case complete with the trigger pawl tripping bolt and its spring. The trigger pawl tripping bolt and its spring can be removed from the spring case by driving out the trigger pawl tripping bolt retaining pin transversely through the spring case.
(h) Drive out the interlock rod guide block retaining pin and press the block out from the breech casing.
(i) Remove the breech pawls by prying out the right and left axis pins. The breechpawls and their springs will then fall out. (j) Lift the end of the hammer plate securing spring clear of the hammer plate and tap the hammer plate upward to remove, (k) Drive out the retaining catch axis bolt and lift out the retaining catch. Drive out the retaining catch plunger pin and remove its spring and the retaining catch plunger.
(l) Drive out in either direction the barrel spring seating ring retaining catch retaining pin. Lift out the retaining catch and its spring.
(m) Press in the breech casing barrel stop pin plate using a pointed tool from tool roll. Drive out, in either direction, the barrel stop pin plate. Lift out the barrel stop pin, the barrel stop pin plate pin, and the barrel stop plate spring.
(n) Push the trigger intermediate lever spring case out by pushing on its rear end at the rear face of the breech casing. Remove the trigger intermediate lever spring case distance piece. Drive out the trigger intermediate lever plunger retaining pin Lift out the trigger intermediate lever plunger and its spring.
2. The complete reassembly instructions given below are a continuation of the reassembling a partially stripped gun.
(a) Place the trigger intermediate lever plunger and its spring, in the trigger intermediate lever spring case. Install the trigger intermediate lever plunger retaining pin. Install the trigger intermediate lever spring case distance piece. Push the real end of the trigger intermediate lever spring case into the rear face of the breech casing.
(b) Install the barrel stop pin plate spring, the barrel stop pin plate pin, and the barrel stop pin. Drive in, from either direction, the barrel stop pin plate.
(c) Install in the breech casing the retaining catch and its spring. Drive in from either direction the barrel spring seating ring retaining catch retaining pin.
(d) Install in the retaining catch the retaining catch plunger its spring and drive in the retaining catch plunger pin. Install the retaining catch in the breech casing and drive in the retaining catch axis bolt.
(e) Tap the hammer plate downward into its recess in the breech casing. Make certain the hammer plate securing spring is in place.
(f) Install the breech pawl springs in the breech casing. Install the right breech pawl and left breech pawl on their spring, installed above. Install the breech pawl axis pins.
(g) Note.--Follow operation 1 of "Reassembling a partially stripped gun" in section H under Reassembling.
(h) Install the trigger pawl tripping bolt spring and the bolt in place in the trigger pawl tripping bolt spring case. Drive the trigger pawl tripping bolt retaining pin transversely through the spring case. Place the spring case (as just assembled) and the trigger pawl tripping bolt spring and tripping bolt in the breech easing. Drive in the trigger pawl tripping bolt spring case retaining pin. This pin secures the spring case to the breech casing.
(i) Install the magazine interlock fork to the breech casing by inserting the fork in its position and drive in its axis bolt from either direction.
(j) Install the safe/fire lever and the safety cam and drive in the axis bolt. Install the safe/fire lever on its axis bolt and drive the axis bolt pin in from right to left. This pin secures the safe/ fire lever to the axis bolt.
(k) Assemble the trigger pawl and its spring to the pawl holder by inserting the pawl axis pin from right to left. Drop this trigger pawl and holder assembly into its position in the breech casing. Insert the trigger crank from inside of the breech casing.
NOTE.--The pawl, pawlholder, and trigger crank are all stamped with the letter "I" and when correctly assembled all three letters must be visible from above. IF NOT VISIBLE, THE ASSEMBLING HAS BEEN INCORRECTLY DONE.
(l) Insert the trigger intermediate lever so as to engage the pin on the pawlholder.
(m) Reassemble the trigger, trigger retaining bolt from inside the breech casing. Install the trigger pin. Reassemble the trigger hook and its spring in the trigger holder and drive in the trigger hook axis bolt.
(n) Place the two outer plungers (parallelogram lever plunger-top) and place the central plunger (parallelogram lever plunger-rear; and their three springs in the parallalogram spring box. Install the horizontal pin that is used to secure the central plunger. Install the two vertical pins that are used to secure the two outer plungers. Reassemble the parallelogram. Install the parallelogram lever axis bolt, top front. Install the parallelo-gram lever axis bolt, bottom front. Install the parallelogram.
lever axis bolt, top front sleeve and the sleeve pin. Install the two retaining pins on the lever axis bolt, bottom front.
NOTE.--The parallelogram levers are all marked "L" and "R". A correctly assembled parallelogram will have all the letters "L" visible and on the left side, and all of the letters "R" visible and on the right side. The parallelogram top lever is marked with the word "Up" and this must be visible from above.
Install the parallelogram spring box assembled above and drive in its axis bolt. Drive from either direction. Place the parallelogram assembled above in the trigger casing, pushing it rearward against the spring plungers in the spring box in order to get the holes in line for the lever axis bolt rear top. A strong push is required. Drive this lever axis bolt in from either direction.
(o) Install the trigger hook holder assembled in Operation 13 into the rear of trigger casing. A strong push is required. Replace the trigger snap ring that secures the trigger hook holder in the trigger casing, using the special pliers in the tool roll. Replace the trigger buffer springs.
(p) Complete the reassembly by following the instructions for reassembly, operations 2 through 9 inclusive, given in detail in section H under Reassembly.
SECTION K. MOUNT
1. The mount permits the height of the gun trunnion above the deck to be easily and rapidly altered for any sight angle, thus enabling the gunlayer to assume the easiest position. This is done by the column-raising handwheel mounted on the pedestal head. A tubular column supports the trunnion bracket and carries an internal thread that mates with a screw, driven by the handwheel. The rotatable pedestal head may be locked in any position by the clamping lever. On the base of the pedestal in also located the bracket for the cocking wire rope.
The gun can be trained through 360° and continued around by means of the rotatable combined trunnion bracket and pivot. There is no stop; therefore, the training can be continued on any target without stopping.
The gun can be elevated from minus 5° to plus 87° by means of the rotatable cradle.
The pedestal of the Mark 4 has two brackets for the cocking wire rope. The wire rope is hooked in the lower bracket for use when cocking the gun. When the gun has been cocked, the upper end of the cocking wire rope is unhooked from the breech bar, wrapped around the pedestal, and hooked over the upper bracket.
The Mark 2 mount has the cocking wire rope attached to a spring-controlled reel that winds up the cocking rope inside the pedestal when it is not in use.
2. There are five principal parts in the mount as follows:
(a) Fixed pedestal supports the mount and is bolted to the deck. A cocking wire rope bracket is bolted to the outside and is used to hook the wire rope on when cocking the gun. A bottom cover plate is bolted underneath the pedestal and is the main support for the equalizing springs, the column-raising spindle and the vertical shaft of the gear train. This bottom cover plate has a shim pack which provides the means of adjustment for free movement of the column. A guide tube is fixed within the pedestal and is provided with a vertical keyway in which slides the key on the tubular column.
(b) Tubular column is constructed with internal threads at its lower end. These internal threads engaged external threads on the column-raising spindle. The handwheel operates the column-raising spindle. The helical springs are inside the column-raising spindle and the pivot and they are placed in series in compression, being separated by a spacing ring. Guide tubes hold these springs, the lower external guide tube being supported by a thrust bearing in a bushing on the bottom cover plate.
CAUTION.--These compressed helical springs must not be disassembled unless a special fixture is used. The heavy compression these springs are under will cause serious injury unless the compression is eased off.
(c) Pedestal head, through which the column rises, is able to rotate around the top of the fixed pedestal but can be held in any desired position by a spring steel clamping band that is oper-ntod by a lever. The pedestal head contains the handwheel drive, a double gear consisting of a bevel apd spur for the purpose of transmitting the drive, and the clamping band with its lever.
(d) Combined trunnion bracket and pivot is free to rotate around the top of the column on thrust bearings, which take upward and downward thrust, and in roller bearings located between the column and the trunnion bracket and pivot. It carries the trunnion arms that have plain bearings for the trunnion pins of the cradle.
NOTE.--Two holes, each being 1 1/2 inches in diameter, are provided in the trunnion arms. These holes are directly above the center of gravity of the mount and a cable through these holes will support the mounting in a vertical position.
(e) Cradle rotates freely about the right trunnion pin. The left trunnion pin is keyed to the cradle in order to form an abutment for the counterbalance torsion spring. This torsion spring is used to compensate the weight of the gun when the gun is in elevation. The gun is carried in two machined and grooved slides in the cradle. The breech casing of the gun is positioned in a fore and aft direction by the gun securing bolt operated from underneath.
3. When gun is being mounted in the cradle, the inside of the securing holt hold in the breech casing and the securing bolt itself should be thoroughly greased for protection against corrosion. Two cavities at the rear of the cradle are filled with lead to act as balance weights. A canvas bag is attached to the cradle to catch the fired cartridge cases.
4. The pedestal head can be turned by hand to any position desired when the clamping lever is raised. The pedestal head can be locked in any position by depressing the clamping lever.
NOTE.--The column raising handwheel tends to turn idly during the rotation of the pedestal head, and the rotation of the head can be assisted by turning the handwheel.
5. When the pedestal head is locked so that it cannot rotate, the action of turning the handwheel drives the gear train. The column has threads that are engaged in the threads of the column raising spindle and is prevented from turning by a key that is in a verticle keyway in the guide tube. The column, therefore, rises with the gun and the weight of the rising parts is taken
by the compressed internal helical springs which aid in raising the gun. The rise of the gun is limited by the upper stop ring secured to the top of the spindle. A. lug on the spindle spur gear acts as the lower stop.
NOTE.--A locking catch is provided to lock the handwheel and thus fix the column at any height. A housing catch is also fitted to lock the combined trunnion bracket and pivot, when It is in its lowest position to the pedestal. A locking bolt enables the cradle to be locked to the trunnion bracket at elevations of plus 5° and plus 87°.
6. There are two ring-shaped internal oil wells. One of these is at the top of the pedestal head and the other is in the head of the pivot of the trunnion bracket.
NOTE.--The oil wells are fitted with spring type dust proof oilers and the wells should be kept filled with ice machine oil.
The trunnion bearings are lubricated by spring ball pressure fittings that are screwed into the upper part of the trunnion bearings.
The following lubrication is necessary during reassembly.
(a) Coat the column raising spindle with grease before assembling it in the pedestal.
(b) Pack grease all around the bevel and spur wheel gear before the pedestal head is installed. Spread grease over all of the teeth of this gear completely covering all the teeth.
(c) Pack grease on the teeth of the handwheel spindle and bevel pinion piling the grease on the face of the gear opposite its spindle before assembling it to the pedestal. d) Pack grease on the teeth of the column raising spindle " spur wheel and vertical shaft spur wheel lower.
(e) Fill the bottom cover with grease before assembling it to the pedestal.
(f) After assembling the bottom cover to the pedestal, complete the filling of the cover with grease by screwing a pressure grease fitting into the pipe tap hole that is in the cover and fill with; grease by using pressure gun.
SECTION L. AMMUNITION FOR 20-MM. ANTIAIRCRAFT GUN MARK 4 OR MARK 2
There are six types of ammunition and they are listed as follows:
(a) High explosive, with tracer; projectile type "HL" loaded with pentolite, an explosive formed by combining equal parts of TNT and PETN. Color of projectile, BLUE.
(b) Same as (a) except projectile is loaded with tetryl. Color of projectile, LIGHT GREY.
(c) High explosive without tracer; projectile type "HB" loaded with pentolite. Color of projectile, YELLOW.
(d) Same as (c) except projectile loaded with tetryl. Color of projectile, WHITE.
(e) Blind loaded with tracer. Color of projectile, DARK GREEN GREY with 1/8-inch wide YELLOW BAND.
(f) Blind loaded and plugged. Color of projectile, DARK GREEN GREY.
NOTE.--The above colorings apply to 20-mm. antiaircraft ammunition only for Mark 4 and Mark 2. Do not confuse with colors used in other ammunition.
(a and b) This projectile has about one-half of the cavity loaded with pyrotechnic tracer mixture designed to burn about 3 3/4 seconds. The forward part of the projectile cavity space is loaded with pressed tetryl or pentolite. These explosives are approximately equivalent in destructive value. The fuze used is a simple air-column type with no moving parts. Its action is initiated by impact, an air-column is instantaneously formed by impact, either head-on or glancing, The closing disk being displaced into the fuze body by impact, an air-column is instantaneously compressed and wire drawn through an inner disk. The rate of temperature-pressure rise is sufficient to ignite lead azide, which in turn ignites pressed tetryl in the detonator, and ignition of the burster charge is affected. The fuze is designed definitely not to function on the equivalent of 0. 012 inch duraluminum plate (or lighter), but definitely to function on the equivalent of 1/8-inch mild steel plate or heavier. The fuze is not equipped with any bore-safe feature, and will act whenever the closing disc is displaced into the fuze with sufficient force. This projectile is not equipped with a self-destruction feature.
(c and d) This projectile is similar to the "Leaded and fuzed projectile with tracer" described above, but has a burster charge that is approximately twice as great.
(e) This projectile has the burster charge cavity inert loaded to weight, except for the tracer, and is plugged at the nose with a fuze body, assembled with no detonator.
(f) This projectile has the burster charge cavity inert loaded to weight, and is plugged at the nose with a fuze body assembled with no detonator.
The powder is an FNH type of nitrocellulose powder. It is a single-perforated grain with weight of charge to give 2,725 foot-seconds at 90° F. with standard projectiles. Surveillance and break-down of 20-mm. antiaircraft cartridges are covered in separate correspondence. Instructions regarding this ammunition are similar to those currently effective regarding 1. 10-inch, 75-caliber ammunition.
The cartridge case is of the usual type with a conventional percussion cap.
SECTION M. GENERAL INFORMATION ON 20 MM.
An HE shell must never be fired through a muzzle cover. To prevent such an occurrence the last two rounds loaded in each magazine should have blind loaded projectiles.
The first shipments of ammunition are being made in wooden boxes. Later shipments will be in metal boxes containing 180 rounds in each box. The completely filled metal box weighs 1.25 pounds. Rounds are packed in separate cardboard tubes and each tube is lined with greaseproof paper so that the grease on the cartridges will not be absorbed. The cardboard tube is open at both ends but is fitted with an inner ferrule, to prevent the cartridges from clearing the tube fuze first. The cartridge is a light friction fit in the tube.
Use care in withdrawing greased cartridges from their packing tubes. The most efficient way of getting them free of the tube is to push on the nose of the fuze with a finger of the hand, while firmly holding the packing tube. As previously stated, there is an inner ferrule in the tube to prevent the cartridge from clearing the tube fuze first. Pushing on the nose of the fuze starts the cartridge out of the tube, when it immediately
becomes a loose fit and care must be taken not to permit the greased cartridge to come adrift and fall.
Stoppages of the gun have occurred which appeared to have been caused by the presence of hair from ammunition packing material getting into the mechanism. Steps have been taken to eliminate this type of packing, but a large amount of ammunition has already been issued. At the first opportunity, and in any event before loading it into the magazine drums, ammunition should be examined to see that it is free of hair; and if hair or dirt is found it should be removed. If grease is removed in this process, it must be replaced.
NOTE.--Pay attention to the need of a complete covering of mineral grease on all cartridge cases.
All 20-mm. antiaircraft Mark 2 and Mark 4 ammunition MUST BE COMPLETELY COVERED WITH A LIGHT COAT OF MINERAL GREASE BEFORE BEING LOADED INTO THE MAGAZINE.
The ammunition is usually packed greased. However, this grease tends to dry off. Whether cartridges are packed greased or not, they should be regreased before loading the magazine.
Note. ---A small amount of mineral grease, applied shortly before firing, to the cartridge case that is visible in the magazine mouthpiece, will assist in preventing a jam in the gun barrel.
Dry ammunition or ammunition with insufficient grease will jam in the gun chamber when fired, and extraction will be very difficult, if not impossible.
NOTE.--Oil must not be used as a substitute for mineral grease.
Sufficient grease should be present on all cartridge cases to be easily felt by the fingers. An excess should be avoided.
CAUTION.--Do not grease the rear end of the cartridge cases as the grease has a tendency to percolate inward past the percussion cap. NEVER USE OIL.
Care must be used in handling the greased cartridges. They must not be dropped or struck a heavy blow on either the nose or the cartridge base. Any cartridge that has been dropped over 5 feet is to be set aside and turned in to any naval ammunition depot at the first opportunity.
NOTE.--Rounds that have been possibly damaged as described above, are not to be considered unsafe, except for firing. If used
for firing, they might result in dud action and, therefore, should be refuzed before firing.
If prolonged firing is necessary, then the cartridge bag should be emptied frequently. A cartridge bag that gets too full, gets in the way of the gun layer at high gun elevations.
Secure, and turn in to a naval ammunition depot, all ammunition boxes, internal containers, fired cartridge cases, packing tubes, dropped or damaged cartridges. The tear strip of the top of the internal container may be discarded.
Chapter 2. BROWNING MACHINE GUN
(.50 CAL., AIR COOLED, M2, BASIC)
SECTION A. GENERAL DISCUSSION
1. The fundamental operating principle of the Browning machine gun, cal. . 50, M2 pattern, is the same as that of cal. . 50 Browning machine guns of previous manufacture. The force of recoil is used to perform the various mechanical operations of the gun. The mechanism consists of a barrel attached to a barrel extension, and a bolt, which are positively locked together when the mechanism is in the forward position. Upon the discharge of a cartridge the energy set up in the barrel starts the action of recoil which is transmitted to the bolt and resisted by the barrel extension. When the mechanism has recoiled 3/4 of an inch, the positive lock between the bolt and barrel extension starts to release and the separation occurs in an additional 3/8-inch travel. The 2 1/8 inch distance of recoil may be considered as the power stroke. Following this separation of the bolt, a portion of the recoil forces in the barrel extension is transmitted to the bolt by an accelerator and the remaining energy to a back plate through a hydraulic buffer mechanism. The energy of recoil of the gun if finally delivered to the mount.
2. The functions of the accelerator are as follows:
(a) To act between the rear surface of the barrel extension and the bottom projection on the bolt as a lever of increasing length to relay recoil energy to the bolt. This utilization of energy serves to slow up the barrel and barrel extension recoil, and to speed up the recoil of the bolt.
(b) To boost the recoil energy of the bolt at the period when extraction occurs.
(c) To hold the barrel and barrel extension in the recoil position, with the oil buffer spring compressed to prevent the barrel returning to its forward position before the bolt has completed its recoil.
(d) To relay energy from the bolt on its forward movement to the barrel extension in order to insure that the barrel extension and the barrel move forward ahead of the bolt so that when the breech lock in the barrel extension rises it will be properly timed with the bolt to insure hooking without binding or interference. That is, the accelerator serves as both an energy transmitter and as a timing element to insure proper closing and locking as well as unlocking of the breach lock from the bolt.
3. Through relayed energy of the accelerator the bolt continues to recoil, compressing its driving spring, and is brought to rest by the back plate buffer. During the recoil of the bolt several functions have occurred, including extraction of the fired cartridge case, and extraction of a live round from the ammunition belt and placing it in position for chambering.
4. The counterrecoil of the bolt, due to the energy stored in its driving springs, begins immediately after the recoil of the bolt has been arrested by the back plate buffer. At this time the fired cartridge case is ejected and chambering of the live round begins. This counterrecoil continues until the bolt trips the accelerator. This tripping of the accelerator causes the counterrecoil of the barrel extension and attached barrel to occur ahead of the bolt. The energy used to trip the accelerator momentarily delays the movement of the bolt, assuring the proper timing for completing chambering of the live round and the positive locking of the mechanism.
5. In order that the trunnion adapter of the aircraft gun may be quickly disassembled from the receiver, a component called the trunnion block shim is provided so that the mating components will be interchangeable without the threads having to be qualified.
(a) There are 12 different thicknesses of trunnion block shims manufactured. They are marked with numbers running consecutively from 1 to 12. No. 1 shim is 0. 0675 inch thick and the thickness of each higher numbered shim is increased by 0. 0025 inch.
(b) Upon original assembly of the machine guns at place of manufacture the shim of correct thickness is assembled and the number of that particular shim and the next three higher numbers are marked on the side plate and the rear oil cap trunnion
adapter or barrel jacket. The three next higher numbered shims accompany the machine gun as a thicker shim may be required later.
Example.--If number 3 shim is used in the machine gun assembly then shims numbered 4, 5, and 6 will accompany the machine gun and the numbers 3, 4, 5, 6 will be marked on the side plate and the rear oil cap.
6. General data.--The following general data applies to all types of Cal. . 50, machine guns. General data pertaining to the individual types of gun are given in this section which covers the particular type.
Caliber inches .50 Weight of 1 metallic belt link (approximate) oz 1/2 Weight of 100 rounds in metallic link belt pounds 50.25 Weight of complete round of M2 ball ammunition (approximate) oz 4 Weight of powder charge (approximate) do 1/2 Weight of bullet, M2 ball (approximate) do 2 Maximum of chamber pressure per square inch pounds 52,000.00 Muzzle velocity of bullet feet per second 2,900.00
7. General data.--Browning machine gun, cal. .50, M2, aircraft.
Weight of gun (fixed mounting) pounds 64.51 Weight of gun (flexible mounting) do 68.51 Weight of barrel assembly (barrel and sleeve) do 9.85 Over-all length of gun (fixed mounting) inches 57.09 Over-all length of gun (flexible mounting) do 56.40 Over-all length of barrel do 36.00 Rate of automatic fire shots per minute 500-650
SECTION B. FUNCTIONING
1. General remarks.--This section outlines the functioning of the Browning machine gun, cal. .50, M2.
2. To load.--Loading may be considered to include two distinct operations, namely, entering the loaded belt properly into the belt opening and thereafter operating the mechanism of the gun until it is closed, with the cartridge in the chamber and
a cartridge in the feedway gripped by the extractor for extraction on the next recoil stroke.
(a) The first of these operations may be performed with the cover either open or closed. In either case, enter the double-loop end of the belt through the feed opening until the first cartridge is beyond the belt holding pawl. Close the cover, if open. Pull the belt completely to the rear by means of retracting slide (operating slide or bolt handle) and release it.
(b) The second operation consists of pulling the bolt once completely to the rear and then allowing it to spring forward. This operation must start with the action fully closed and the extractor gripping the cartridge in the feedway.
3. To unload.--(a) Lift cover, remove belt, retract bolt, and make visual inspection of feedway, T-slot, and chamber, to make Certain that the gun is unloaded.
(b) Release belt and lower cover.
(c) Press the trigger or sear mechanism to relieve tension on the firing pin spring.
4. Backward movement of recoiling parts.--(a) The explosion of the cartridge forces the barrel to the rear, carrying with it the barrel extension and the belt which is locked to the barrel extension by the breech lock.
(b) When the barrel has recoiled about % inch, the breech lock pin strikes the cam surfaces of the breech lock-depressors. This unlocks the belt from the barrel extension and permits the belt to continue to the rear.
(c) As the barrel extension moves to the rear it strikes the accelerator and turns it backward.
5. Backward action of the accelerator.--(a) As the accelerator turns backward it strikes the bottom projection on the bolt and accelerates it to the rear.
(b) The shoulders on the barrel extension shank engage behind the claws of the accelerator, locking the barrel and barrel extension in a rearmost position, to the oil buffer body.
6. Backward movement of the bolt.--(a) As the bolt moves backward the driving springs are compressed.
(b) The bolt brings with it a cartridge from the belt gripped by the extractor and an empty case from the chamber gripped in the T-slot.
(c) The cam lug on the extractor rides along on top of the switch until near the end of the backward movement of the bolt, then the extractor by action of the cover extractor cam is forced downward until its cam lug is below the switch.
7. Action of the oil buffer.--As the barrel and barrel extension move backward together, and since the oil buffer piston rod is linked directly with the barrel extension by means of the hook on the shank projecting from the rear of the barrel extension and the hook on the forward end of the oil buffer piston rod, the oil buffer spring is compressed, the oil buffer piston rod head and the oil buffer piston valve are driven rearward in the oil buffer tube forcing the oil through the restricted openings in both the piston rod head and valve, uncovering the openings and permitting the oil to pass readily from the forward to the rear side of the piston rod head and valve, thus permitting the rapid return of the parts to the firing position.
8. First action of feeding.--(a) As the bolt moves backward, the stud on the belt feed lever, riding in its cam groove in the top of the bolt, moves the belt feed pawl laterally into position behind the next cartridge.
(b) The ammunition belt is prevented from falling out of the gun by the belt holding pawl.
9. (a). As the bolt moves backward, the upper end of the cocking lever is forced forward by the top plate bracket attached to the top plate, which brings the lower end to the rear.
(b) When the lower end of the cocking lever moves to the rear it brings with it the firing pin extension, withdrawing the firing pin from the face of the bolt and compressing the firing pin spring against the sear stop pin.
(c) The shoulder of the firing pin extension, engages in the notch in the sear under pressure of the sear spring.
10. Action of the driving springs.--When the rear end of the bolt strikes the buffer plate, its remaining force is absorbed in the fiber buffer discs. The driving springs, which have been compressed by the backward action of the bolt, then force the bolt forward. On guns manufactured after June 1940 two driving springs, one inside the other and wound in opposite
directions, are used. By use of two springs, greater initial Spring load is provided which is an advantage in feeding ammunition during high angles of fire. The new assembly will be available for replacement of old type assemblies now in service.
11. Forward movement of the bolt.--(a) When the bolt starts forward the cam lug on the extractor riding under the switch rotates the extractor downward. This causes the extractor to force the cartridge down the T-slot in line with the chamber. If there is an empty case in the T-slot, the live round, held by the extractor and ejector, or the ejector if there is no live round, strikes the empty case at this point and forces it out of the T-slot.
(b) The upper end of the cocking lever is forced backward and the lower end moves forward away from the rear of the firing pin extension.
12. Release of recoiling parts.--(a) The bottom projection on the bolt strikes the accelerator and rotates it forward. This unlocks the barrel extension from the oil buffer body. The barrel extension remains linked with the oil buffer piston rod.
(b) When the accelerator has been tripped the barrel extension and the barrel move forward, assisted by the oil buffer spring.
(c) Part of the forward force of the bolt acts through the accelerator to push the barrel extension forward.
13. Loading and locking action.--(a) The extractor rises as its cam lug moves along the top of the extractor cam and the ejector moves outward, leaving the cartridge in the chamber engaged by the T-slot. The extractor grips the first round in the belt and is held down firmly, ready to extract it, by the cover extractor spring.
(b) The breech lock is forced upward by the breech lock cam and locks the breech just before the recoiling parts reach the firing position. (The breech lock engages in a recess cut in the bottom of the bolt and thus locks it firmly to the barrel extension and against the rear end of the barrel. )
14. Second action of feeding.--(a) As the bolt goes forward the stud of the end of the belt feed lever, riding in its cam groove in the top of the bolt, moves the belt feed slide and belt feed pawl in a lateral direction.
(b) The belt feed pawl carries the first cartridge against the cartridge stops, ready to be gripped by the extractor.
NOTE.--The aircraft guns use the cartridge alining pawl when feeding from the left side. The cartridge alining pawl is not reversible and when aircraft guns are fed from the right the old design rear cartridge stop, not having the cartridge aline pawl, is used.
(c) The next cartridge is carried over the belt holding pawl, which rises behind it and holds it in position to be engaged by the belt feed pawl on its return movement.
15. Trigger action in automatic fire.--If the side plate trigger is held to the rear, the sear is disengaged just before the bolt has reached its forward position, thereby releasing the firing pin extension. The gun thus fires automatically, repeating the operating of functions already described. (The release of the firing pin extension actually takes place when the recoiling parts are still about 1/8 inch from the forward position but after the breech is locked. )
16. Adjustment of oil buffer.--(a) The oil buffer is so arranged that it is possible to adjust the speed of the firing of the machine gun. This is accomplished by turning the oil buffer tube the required number of clicks, depending on whether a high rate of fire is desired or a slower rate.
(b) Turning the buffer tube to the right tends to cut off or close the oil buffer which allows it to absorb more recoil and reduce the rate of fire.
(c) Turning the buffer tube to the left allows the oil buffer to open and allows the oil to pass through larger throttling parts which results in an increased rate of fire.
(d) Guns of early manufacture were equipped with a regulator having an index finger. The index finger has a key which fits into a slot in the rear of the buffer tube. The letter "O" on the left side of the back plate indicates the "open position" for the oil buffer and the letters "CL" on the right side indicates the "closed position. " Turning the index finger to the right or left opens or closes the oil buffer as desired.
(e) Guns of new manufacture have a hole in the back plate through which the oil buffer may be adjusted with a screwdriver blade.
SECTION C. DISASSEMBLING, HEADSPACE ADJUSTMENT, REPLACING GROUPS IN GUN, AND METHOD OF CHANGING AIRCRAFT GUN FROM LEFT-HAND FEED TO RIGHT-HAND FEED
1. General information on disassembling.--(a) Disassembling will be considered under two general headings: Removal of groups to the extent required for ordinary cleaning and for minor repairs, and detail disassembling, involving removal of all components from each group.
(b) A group is a number of components which either function together in the gun or are intimately related to each other and should, therefore, be considered together.
(c) The removal of groups is outlined in this section as the procedure is similar for the water-cooled antiaircraft guns.
(d) Detail disassembling is outlined in subsequent sections which cover the particular type of gun.
2. Removal of groups from gun.--(a) Release the cover latch and open the cover. The cover need not be removed as the other parts of the gun may be taken out without removing it.
NOTE.--Removal of the cover group is not recommended unless necessary for repair as it is difficult to reassemble due to the force required to compress the detent pawl spring.
(b) Release back plate latch lock and back plate latch and lift out the back plate.
(c) Press forward and away from the side plate on the end of the driving spring rod to release retaining pin in head of rod from hole in side plate. Draw bolt to the rear until the bolt stud is in line with hole in center of slot in side plate. Remove bolt stud from bolt.
(d) Remove the bolt, complete, out of the rear end of the gun casing. The assembled driving spring unit need not be removed from the bolt.
(e) Compress oil buffer body spring lock, using a cartridge point or a drift through hole in right-hand side plate and remove oil buffer, barrel extension, and barrel assembly by pulling out to the rear.
NOTE.--When the guns are mounted in a close or remote position the release tool is used to compress the oil buffer body spring lock.
(f) Detach the oil buffer assembly from the barrel extension by pressing the accelerator forward.
3. Headspace.--The headspace of a military weapon with a cartridge fully seated in the chamber is the distance between the base of the cartridge and the face of the bolt. In Browning machine guns, the headspace is adjusted by obtaining the proper distance between the forward part of the bolt and the rear end of the barrel. The headspace adjustment must be checked before firing.
4. Head-space adjustment.--(a) In the past the head space has been adjusted with the barrel, barrel extension, and bolt out of the gun. However, the best adjustment is obtained with the gun fully assembled. This method has the additional advantage of avoiding the loss of the cooling liquid.
(b) To adjust the head space.--Unscrew the barrel from the barrel extension until the action works freely. Then using the point of a cartridge screw the barrel into the barrel extension until the action will just close without being forced. Then unscrew the barrel TWO ADDITIONAL notches.
CAUTION.--Care must be exercised to avoid roughening the barrel surface during adjustment. Care must also be exercised on water-cooled guns to eliminate binding of the barrel by the packing, or a false adjustment may otherwise be obtained.
5. Effect of head-space adjustment.--Probably the most important adjustment of the machine gun is the head-space adjustment. Tests show that shot patterns are not adversely affected by the head space when the guns are adjusted as outlined above. In fact, better uniformity of shot patterns will be obtained when the guns are operated with the above adjustment which is based on the fundamental design of the weapon. Tests have also proved that guns may be damaged and in some cases put out of action by using unapproved methods of adjusting the head space. Many reports show that difficulties with improperly guided belts and with firing mechanisms have been attributed to undue concern over head-space adjustment.
(a) Insufficient headspace.--When the head-space adjustment is too tight, poor functioning will result as the breech lock will not fully enter its recess in the bolt. This condition may damage the barrel extension, bolt, or breech lock. Extraction trouble may also occur due to improper timing of locking and unlocking.
Furthermore, with a tight head-space adjustment the gun operates sluggishly because of the binding of the moving parts.
(b) Excessive head space.--If the head space is too great, a separation of the cartridge may occur. Should there be any weakness in the base of the cartridge case, such as a split case, the possibility of a rupture is increased by excessive head space.
NOTE.--When assembled correctly for right-handfeed, the enlarged portion of the bolt switch is toward the rear of the bolt.
(c) Assemble extractor assembly to bolt.
6. Belt feed mechanisms.--(a) Open cover and remove belt feed lever. Transfer the belt feed lever plunger and spring from upper hole in belt feed lever to lower hole.
(b) Remove belt feed slide assembly from cover.
(c) Drive out belt feed pawl pin and remove belt feed pawl and arm from the belt feed slide.
(d) Hold the belt feed pawl with the arm pointing toward the body (spring seat in pawl up and arm down) and change the belt feed pawl arm from left side of pawl to the right side of pawl.
(e) Reassemble belt feed pawl and arm to belt feed slide.
(f) Reassemble belt feed slide assembly to cover, with belt feed pawl arm pointing toward left side of gun. (g) Reassemble belt feed lever to cover.
7. Gun casing.--(a) Remove belt holding pawl pins from right and left sides.
(b) Transfer the front rear cartridge stops and the link stripper from the right to the left side of the gun.
NOTE.--Guns of new manufacture when fed from the left side have a rear cartridge stop assembly which cannot be used when the gun is fed from the right side. In changing from left- to right-hand feed it is necessary to substitute a rear cartridge 1stop and stripper of old design. The rear cartridge stop assembly referred to above has a cartridge alining pawl which prevents "short round" stoppages.
(c) Transfer the belt holding pawl and belt holding pawl spring from left side of gun to right-hand side.
(d) Assemble the belt holding pawl pins to the gun.
(e) Assemble the bolt assembly in the gun and complete the assembly of the gun in the usual manner.
8. Inspection before firing gun.--After changing the gun from left-hand feed to right-hand feed, or vice versa, and also before firing, the gun should be inspected in order to determine that it has been properly assembled. Note should be made of the following when the gun is arranged for right hand feed:
(a) When the cover is open the upper end of the belt feed lever should position itself toward the right-hand side of the cover.
(b) The belt feed pawl arm should point toward the left with the arm assembled to the upper side of the pawl (cover raised).
(c) The front and rear cartridge stops and the link stripper should be assembled on the left side of the feedway.
(d) The belt holding pawl should be in position on the right side of the feedway.
(e) Looking down on top of the bolt as it is assembled in the gun, the enlarged portion of the bolt switch should be toward the rear.
9. Cooling.--Aircraft machine guns are air-cooled and as mounted at present there is very little difference in the cooling whether the gun is fired on the ground or in the air.
(a) With the standard 36-inch cal. .50, M2 barrel weighing 9. 85 pounds, a maximum burst of 75 rounds may be fired from a flexible gun. Approximately one minute after firing a 75-round burst, firing may be resumed and 20 rounds fired and repeated each minute thereafter.
(b) The long burst will heat the barrel to the maximum permissible temperature, and repeated firing after one minute delay with a reduced number of rounds per minute will maintain the barrel at the high temperature. Thus the initial burst of 50 to 75 rounds or a 50- to 75-round burst followed by firing 20 rounds for each succeeding minute, requires a cooling time or cessation of fire for approximately 15 minutes before the long burst can be repeated.
(c) If long bursts are not fired, approximately 25 rounds may be fired each minute over long periods.
SECTION D. CARE AND CLEANING
1. General care.--The importance of a thorough knowledge of how to care for and clean the machine gun can not be over-
emphasized. The kind of attention given to a weapon of this type determines largely whether or not it will shoot accurately and function properly when needed. The bore and chamber must be kept in perfect condition for accurate shooting. Also, it is just as important that the receiver and moving parts be kept clean, lubricated, and in perfect condition for efficient functioning. Care and cleaning will not be confined to the gun alone but will include all accessories. Belt links and ammunition must be kept clean and dry.
2. Cleaning, cleaning materials, and lubrication.--
(a) Cleaning bore.--Disassemble groups from gun.
(1) Place barrel, muzzle down, in a vessel containing hot water and issue soap, a sal soda solution, or lacking these, hot water alone.
(2) Insert cleaning rod, with a flannel patch assembled, in the breech. Move rod forward and back for about one minute, pumping water in and out of bore.
(3) Use a brass or bronze wire brush while the bore is wet, running it forward and back through the barrel three or four times.
(4) Pump water through bore again to clean.
(5) Dry the cleaning rod and remove barrel from water. Using dry, clean flannel patches, thoroughly swab bore until it is perfectly dry and clean. Thoroughly dry and clean the chamber using a flannel patch on a stick if necessary.
(6) Saturate a patch with sperm oil and swab bore and chamber with the patch. Allow a thin coat of the oil to remain in the bore.
(7) Guns should be cleaned not later than the evening of the day on which the gun is fired.
(8) Inspect and clean the guns for 3 days following cessation of firing.
(b) Cleaning parts other than gun.--(1) Wipe receiver clean, care being taken to remove dirt from belt holding pawl. Thoroughly clean cover, bolt, barrel extension, oil buffer, and back. plate, using a small stick covered with a flannel patch to remove dirt from all recesses.
(2) Wipe all parts with an oily rag.
(c) Preparation for storage.--(1) Clean and prepare the guns with particular care. All parts of the gun should be cleaned
and wiped thoroughly dry with rags. In damp climates particular care must be taken to see that the rags are dry. After drying, the bare hands should not touch the parts; handle with an oily rag.
(2) Apply rust-preventive compound to all metal parts of the gun. Rust-preventive compound, medium (U. S. A. Spec. 2-84A) , is a sluggish liquid which pours at a temperature of 81° F. It is used for short-time protection and should not be used on, guns put in permanent storage. It may be applied with a brush or by dipping. In applying, heating is not necessary except in very cold temperatures. Application of the rust-preventive compound to the bore of the machine-gun barrel is done best by dipping the cleaning brush in rust-preventive compound and running it through the bore two or three times. Prior to placing the weapon in storage the bolt should be in the forward position with the firing pin released. In fact it is good practice to relieve the firing-pin tension whenever the weapon is not in use.
(3) The wooden supports in the packing box must be painted with rust-preventive compound before storing the gun. Place the gun in the wooden packing box, handling the gun with oiled rags.
(d) Guns received from storage.--Machine guns received from storage are completely coated with rust-preventive compound. Use dry-cleaning solvent to remove all traces of this grease, particular care being taken that all recesses in which springs or plungers operate are cleaned thoroughly. After using the dry-cleaning solvent make sure it is completely removed from all parts by washing with soap and water, and drying thoroughly. The bore and chamber of the barrel must be thoroughly cleaned. All surfaces having been thoroughly cleaned they should then be protected with a thin film of lubrication oil applied with a rag.
OTE.--Failure to clean the firing pin and driving spring and the recesses in the bolt in which they operate may result in gun failure at normal temperatures, and will most certainly result in series malfunctions if the guns are operated in low temperature areas as rust-preventive compound and other foreign matter will cause the lubrication oil to congeal or frost on the mechanism.
(e) Lubricant to be used on gun.--(1) Proper oiling is second in importance only to intelligent cleaning. It is a vital necessity for the working parts but should be used sparingly. Oil all bearing surfaces of gun before firing, taking particular care to see that exterior of barrel is oiled at breech end, also that cover extractor spring, cover extractor cam, and cover detent pawl are oiled. Oil cocking lever, groove in the bolt for belt feed lever, grooves in barrel extension to take bolt ribs, breech lock cam, switch, extractor cam, sear mechanism, and the Ways of belt feed slide.
CAUTION.--In oiling aircraft guns, special care should be taken not to use an excess of oil, as low temperatures that may be encountered will thicken the oil and may cause the gun to malfunction. The parts are best oiled by wiping with a well-oiled rag. (2) If the gun is to be fired in areas where the temperature is 45° or above, sperm oil should be used, when available. When not available, motor oil, weight 20, or any light grade machine oil, may be used in an emergency.
(3) On all types of machine guns when operated in areas where the temperature is below 45° F., and all aircraft machine guns when operated in the air, regardless of ground temperature, aircraft-instrument and machine-gun lubricating oil should be used.
(f) Preserving machine guns after rust-preventive compound has been removed.--Sperm oil is the most suitable oil for preserving the mechanism when in regular or intermittent use. This oil is efficient for preserving the polished surfaces, the bore and the chamber for a period of from two to six weeks, dependent on the climatic and storage conditions. Aircraft instrument and machine gun lubricating oil should not be considered as a suitable preservative; however, for aircraft guns and other guns operated regularly in cool areas it should be used, and application made more often, as it is a material disadvantage to use sperm oil or other heavy bodied oils, as it is absolutely essential that such oils be removed with cleaning fluid, and aircraft instrument and machine gun lubricating oil applied before an attempt is made to fire the gun in such areas. Sperm oil should invariably be used for preserving the chamber and bore, however, as the light oil cleaning compound is used to remove fouling from the barrel and other parts of the gun.
(g) Rust-preventive compound.--This is a heavy dark-colored sticky grease provided to protect metal surfaces of the gun from corrosion while in storage. It is not a lubricant and should not be used as a lubricant. The compound is of two grades, i.e., heavy and medium.
(1) Rust-preventive compound, heavy (Spec. U. S. A. 2-82B) , must be made fluid prior to use. A practical method to obtain fluidity is to place container in a vessel of water, heating it to a temperature of not over 180° F., the exact temperature being determined by the thickness of the film desired. In no case should it be heated above 180° F. ; at this temperature deterioration of the compound sets in. The higher the temperature of the compound, the thinner is the film applied to the metal. The compound should be heated to the temperature at which used for about half an hour before using. Best results will be obtained if the compound is heated to 180° F., and then allowed to cool to the desired consistency before using. The best method of applying the compound is by dipping as there is much less danger of the inclusion of air bubbles in the grease film by this method.
(2) Rust-preventive compound, medium (Spec. U. S. A. 2-84A) , is a sluggish liquid which pours at a temperature of 81° F. It is used for short time protection and should not be used on guns put in permanent storage. It may be applied with a brush or by dipping. In applying, heating is not necessary, except, in very cold temperatures. Application of the rust-preventive compound to the bore of the machine gun barrel is best done by dipping the cleaning brush in rust-preventive compound and running it through the bore two or three times.
NOTE.--Navy slushing compounds of similar grades may be used.
(h) Metal fouling solution.--This is a perishable mixture; to be prepared as needed, and used for dissolving primer residue and metal fouling from the bores of machine gun barrels.
Prepare the solution as follows:
(1) Ingredients.--Ammonium persulphate, 1 ounce or 2' medium heaping tablespoonfuls, ammonium carbonate, 200> grains or 1 heaping tablespoonful; ammonia (28 percent) , 6 ounces or 3/8 pint or 12 tablespoonfuls; water, 4 ounces or 1/4 pint. or 8 tablespoonfuls.
NOTE.--The foregoing amount is sufficient for cleaning about six machine gun barrels.
(2) Powder the ammonium persulphate and ammonium carbonate together (place them inside a clean cloth and grind with a tool handle) ; dissolve in the water and add the ammonia: mix thoroughly until about 90 percent of the powder is dissolved and allow to stand for one hour before using. The solution should be kept in a strong bottle, tightly rubber corked, and in a cool place. The solution shall be used within 30 days after mixing and should not be used more than twice. Used solution should not be mixed with unused solution but should be bottled separately.
(i) Ammonia swabbing solution.--This is a dilute metal fouling solution used for swabbing out the bores of machine gun barrels. Prepare the solution as follows:
(1) Ingredients.--Ammonium persulphate, 60 grains or 1/2 tablespoonful, smooth off. Ammonia (28 percent) , 6 ounces or 3/8 pint or 12 tablespoonfuls. Water, 4 ounces or 1/4 pint or 8 tablespoonfuls.
(2) First dissolve the ammonium persulphate in the water, then add the ammonia. Keep the solution in a strong bottle, tightly rubber corked, and in a cool place. Pour out that which is necessary at the time only, and keep the bottle corked.
3. Points to be observed, before, during, and after firing.-- When the machine gun is to be fired, it must be cleaned, properly assembled, and lubricated. While in use it must be kept as nearly as possible in the same condition. After firing it must again be put in readiness for later use, Certain rules, the observance of which will aid fulfillment of these conditions, are called points to be observed before, during, and after firing.
a. Points to be observed before firing.--The gunner must be thoroughly impressed with the value of observing these points and testing his gun by their observance each time it is to be fired, doing it, furthermore, before the moment for firing has actually arrived. They are not intended as a guide for a detailed inspection of the gun, nor should points to be observed before firing be so considered. They are intended to constitute a procedure that can be carried out quickly as a preliminary to
going into action with the gun or firing a score at target practice with it.
(1) See that the bore is clear and clean.
(2) See that the working parts of the gun are oiled.
(3) See that oil buffer tube is filled with oil.
(4) See that the adjusting screw is screwed in tight against buffer disks in back plate.
(5) Try gun action several times by hand to see that the mechanism works freely and smoothly.
(6) Test headspace adjustment.
(7) Examine the gun for leakage or excessive friction of the barrel packing. Adjust the packing adjusting ring and muzzle gland, if necessary. Test adjustment of packing by operating the gun by hand. A wide adjustment of the formed packing is provided, and the gun will rarely need repacking.
(8) Verify cleanliness of the sights and tightness of their adjusting screws.
(9) See that water jacket is filled and that the hose connections are tight.
(10) See that ammunition belts are clean and correctly loaded. Secure sufficient supply of ammunition.
(11) Verify presence of tools and spare parts.
b. Points to be observed during firing.--It is to be understood that these points are observed as occasion arises or opportunity during cessation of fire permits. Firing is not interrupted merely for the purpose of observing them.
(1) Clean bore and chamber.
(2) In case of misfire (with bolt fully forward and firing pin released) wait ten (10) seconds before pulling bolt to the rear, for to extract a cartridge having a hangfire is hazardous to personnel and might cause irreparable damage to the gun.
c. Points to be observed after firing.--(1) Unload the gun.
(2) Clean bore and chamber. Inspect bore each day for several succeeding days and clean until all signs of fouling have been eliminated.
(3) Disassemble and clean gun thoroughly. Inspect all parts. Make needed repairs and replacements.
(4) On assembling, check the Operation with dummy cartridges and release the firing pin spring, after insuring that functioning and adjustments are correct.
4. Precautions to be observed in cold weather.--
a. Test the gun frequently to see that it functions properly. b. During cold weather when the gun is silent, the movable parts in the receiver of the gun must be kept absolutely dry and free from oil but before firing the gun the moving parts should be oiled.
5. Precautions to be observed during a gas attack.--
a. Cover guns with waterproof sheet if available.
b. Work recoiling parts if the gun is not being fired.
c. Guns should be cleaned as soon as possible after a gas attack.
d. Oiling will prevent corrosion for about 12 hours.
e. Clean all metal parts in boiling water containing a little soda.
f. All traces of gas must be removed from ammunition with a slightly oiled rag, then thoroughly dry ammunition.
g. Rust-preventive compound resists gas corrosion more than lighter oil.
6. Method of filling oil buffer.--Remove the two oil buffer tube filling screws from the base of the buffer tube. Use the oil buffer filling oiler filled with machine gun recoil oil (Spec. U. S. A. 2-77). In an emergency any light recoil oil may be used, adding glycerin in freezing temperatures if necessary. Start the flow of oil by pressing on the base of the oiler. While the oil continues to pour from the oiler, insert nozzle into either filling hole and with a continued pressure, on the base of the oiler allow oil to flow into the buffer tube. DO NOT RELEASE PRESSURE ON OILER UNTIL NOZZLE HAS BEEN REMOVED PROM PILLING HOLE, THUS AVOIDING GETTING AIR BUBBLES INTO THE BUFFER TUBE. Repeat the operation until the buffer is overflowing. Replace the filling screws. Any excess oil in the buffer will be relieved by the relief valve in the forward end of the buffer body. The reason that two filling holes are provided is to show visually by overflow when the buffer tube is completely full.
SECTION E. MALFUNCTIONS
1. Explanation.--(a) A malfunction is an improper action of some part of the gun resulting in a stoppage; for example, a failure to extract the empty cartridge case.
(b) Any accidental cessation of fire is a stoppage. It may bo a faulty cartridge or a malfunction of some part of the gun. The fact that all the ammunition in the belt being fed into the gun has been exhausted should not be called a malfunction since it is a cessation of fire from natural results.
(c) Immediate action is the term applied to that operation required to clear a temporary stoppage.
2. Prevention of stoppages.--Proper care of the gun and attention to the points before, during, and after firing as outlined before will greatly reduce liability to stoppages, particularly if the gunner has an intelligent understanding of the reasons why stoppages generally occur. Prevention is the best remedy for all stoppages. Nevertheless, stoppages will occur in spite of all that can be done to prevent them.
3. Classes of stoppages.--Stoppages may be classed under two main headings:
(a) Temporary, which are due to--
- Failure of some part of the gun of which a duplicate is carried.
- Faulty ammunition.
- Neglect of points before or during firing.
- Lack of knowledge of the operation and functioning of the gun.
(b) Prolonged, which are due to a failure of some part that cannot, as a rule, be remedied by the gun squad under fire or without skilled assistance.
4. Classified table of stoppages.--(a) Stoppages are classified according to the position in which the bolt stud is found when the gun stops firing.
- Firing position.--Bolt stud all the way forward.
- Second position.--Bolt stud just in rear of all the way forward to half way back.
- Third position.--Bolt stud just in rear of half way back to all the way back.
(b) A table of stoppages classified according to the position of the bolt stud follows:
Classified table of stoppages
Position of bolt stud:
- Misfire due to defective primer.
- Short or broken firing pin.
- Weak or broken firing pin spring.
- Faulty engagement of firing pin and sear notch.
- Sear spring weak, broken, or out.
- Belt improperly loaded. (May cause a second position stoppage. )
- Short round.
- Bent or worn belt feed lever. (May cause a second position stoppage. )
- Belt feed pawl spring weak or out.
- Belt feed pawl pin out or partially out.
- Cover extractor spring weak or out.
- Belt feed lever bent or bolt switch defective. (Stud on end of lever jumps out of cam groove in bolt. )
- Damaged extractor. (May cause a second stoppage. )
- Belt holding pawl out or spring weak.
- Beit holding pawl fails to depress. (May cause a third position stoppage. )
- Separated case which stays in the chamber when bolt is pulled to the rear.
- Separated case which is removed from the chamber by the new round when bolt is pulled to the rear.
- Separated cases due to too much headspace. (May result in either 1 or 2 above. )
- Headspace adjustment too tight.
- Broken or missing barrel locking spring. (May result in either 3 or 4 above. )
- Bulged round.
- Tight link in belt.
- Bullet loose in cartridge case.
- Broken extractor or ejector.
- Battered or thick rim of cartridge.
- Broken cannelure.
- Enlarged hole in recoil plate. (Setback primer. )
- Belt feed pawl arm bent or broken.
- Broken or damaged T-slot in bolt.
- Thin rim of cartridge permitting nose of bullet, to drop below the chamber.
5. Immediate action.--Immediate action is the immediate and automatic application of a proper remedy for a machine-gun stoppage. When a stoppage is experienced, first note the position of the bolt stud. Never push the bolt forward. Proceed as follows:
(a) Gun fails to fire.--With hand, feel rounds entering feed-way. Straighten, if required. See that cover is latched. Wait ten (10) seconds then pull bolt to the rear twice and release it. Relay and fire.
(b) Gun still fails to fire.--(1) Raise cover and note position of bolt. If bolt is not closed, pull back bolt and remove cartridge in T-slot. Examine it. (If cartridge is warm let it cool for about 30 seconds. ) Take first round out of belt. Reload. Relay and fire.
(2) If bolt is closed, pull bolt to the rear once. If a cartridge is ejected, examine for broken firing pin. If no cartridge is ejected, examine feed mechanism and extractor and remedy defect. Reload. Relay and fire.
CAUTION.--After any stoppage which appears to be caused by insufficient recoil, make sure that the bore is clear before continuing firing. It is possible that such a stoppage, as for instance, one caused by incomplete ignition of the powder charge, may result in the bullet lodging in the bore, and in case this happens and another round is fired before the bore is cleared the gun will certainly be seriously damaged.
6. To remove a cartridge from the T-slot.--(a) Hold back the bolt and raise the extractor. The cartridge will usually fall out unless it has a thick rim or the T-slot is defective.
(b) If the cartridge will not fall out when the extractor is raised, use a screw driver or similar tool. Hold the bolt to the rear with the extractor raised. Place the screw driver through
the top of the receiver into the top of the cannelure of the cartridge and drive the cartridge downward out of the T-slot by-striking the upper end of the screw driver with the palm of the hand.
7. To remove a case from the chamber.--If there is an empty case with broken rim stuck in the chamber, hold back the bolt and remove cartridge from the T-slot if there is one. Insert the cleaning rod from the muzzle and knock the empty case from the chamber. If several cases stick in the chamber in close succession put some oil on the chamber and with a cleaning brush, thoroughly scrub the chamber with the brush, then wipe out the chamber with a dry rag.
8. Replacing damaged parts.--(a) Damaged parts will be removed and replaced as quickly as possible. If it is imperative that fire be maintained or immediately resumed, a broken minor part should be replaced by substituting the complete spare part which contains it. Thus a broken firing pin would be remedied by changing bolts; a broken ejector by changing extractors. Later, as opportunity permits, the small parts will be repaired or replaced in order to make the larger part again available for use. Where the complete bolt has been changed, a check should be made on headspace.
(b) It is of extreme importance that all pieces of broken parts be removed when remedying a stoppage due to a broken part. Otherwise, serious damage to the "action" may result on resuming fire.
Chapter 3. THOMPSON SUBMACHINE GUN
SECTION A. DESCRIPTION
1. General.--The Thompson submachine gun, caliber .45, M1928A1 (fig. 19), is an air-cooled, recoil-operated, magazine-fed weapon weighing about 15% pounds with loaded 50-round magazine. The exterior surface of the rear portion of the barrel contains a series of annular flanges which serve to dissipate heat and cool the barrel during firing. The hand of the gunner is protected on the under side of the barrel by a wooden fore grip. A rear grip is also provided. Sling swivels are attached to the fore grip and stock for attaching the gun sling. The weapon is provided with a "Cutts" recoil compensator to lessen the recoil and the tendency of the muzzle to rise in full automatic fire. By correctly setting the rocker pivot, the weapon may be used for either full-automatic or semiautomatic fire. The weapon is fed from a drum-type magazine having a capacity of 50 rounds or from a box type magazine having a capacity of 20 rounds.
2. General data.--a. Dimension:
Diameter of bore inches 0.45 Number of grooves 6 Twist in rifling, uniform, right, one turn inches 16 Length of barrel inches 10.50
Over-all length of gun including compensator. inches 33.69 Sight radius do 22.30
Gun without magazine pounds 10.75 Loaded 20-round magazine do 1.31 Loaded 50-round magazine do 4.95 Empty 20-round magazine do .38 Empty 50-round magazine do 2.63
3. Miscellaneous data.
Initial velocity feet per second. 802 Pressure in chamber (approx.) pounds per sq. inch 12,000-16,000 Weight of ball cartridge (approx.) oz 3/4 Weight of bullet (approx.) do 1/2 Weight of powder charge (approx.) grains. 5 Rate of automatic fire (cyclic rate) shots per minute 600-700
SECTION B. DISASSEMBLING AND ASSEMBLING
1. General.--(a) Disassembling is considered under two general headings, removal of groups and disassembling of the groups.
(b) A group is a number of components which either function together in the gun or are intimately related to each other and should therefore be considered together.
2. Removal of groups from gun.--(a) Magazine.--With the bolt in the rearward position, raise magazine catch and slide out magazine.
(b) Stock.--Press in on butt stock catch button and slide butt stock to the rear.
(c) Frame from receiver.--Turn safety to "fire" position and rocker pivot to "automatic" or "full auto" position. Pull trigger and allow bolt to go forward gradually by retarding actuator with left hand. Place gun upside down on knee or table, muzzle to the left. With thumb of right hand depress frame latch and with left hand slide frame toward rear of gun about 1 inch by pushing or tapping on rear grip. Take gun from table or knees, turn it right side up, grasp receiver firmly with left hand near feedway. With right hand grasp grip in normal firing position, index finger on trigger. Pull the trigger as in firing and withdraw frame to rear of gun, pulling down on frame as well as to the rear as it is withdrawn. Failure to pull down as frame is withdrawn causes frame latch to strike against the rear portion of the trigger and trip, damaging these parts.
(d) Recoil spring.--Support muzzle of barrel on table or knees with open side of receiver facing operator. Grasp receiver with left hand with thumb in position to depress buffer pilot. With thumb of left hand press down on buffer pilot. With thumb and forefinger of right hand engage flange of buffer and pull down until buffer pilot clears back of receiver. If breech oiler follows, push it back. Hold buffer with thumb and forefinger of right hand and withdraw this entire unit from receiver. Care should be taken to obtain a firm hold on the buffer to prevent the recoil spring, which is compressed, from forcing it out of the operator's hand. When the recoil spring, at rest, measures less than 101/2 inches it should be replaced.
(e) Bolt, lock, and actuator.--Grasp receiver, bottom up, with left hand. Slide bolt to the rear and lift out. Slide actuator with lock forward and lift out lock. Slide actuator to rear, turn receiver over, and allow actuator to fall out into right hand.
(f) Breech oiler.--Hold receiver upside down in left hand, muzzle to front. Hook end of forefinger of right hand under front end of right side of breech oiler. Pull up and to left until right side of breech oiler is out of groove in receiver. Hold the oiler in this position with the right thumb. Without moving thumb, hook forefinger of right hand under front end of left side of oiler, and pull oiler out of groove in left side of receiver. With forefinger of right hand pull entire front end of oiler up and to the rear. Lift the oiler out of the receiver, front end first. It is not necessary to remove oiler for ordinary cleaning purposes.
3. Disassembling of groups.--(a) Magazine, 50-round.-- Remove winding key and lift off cover. Lift up on end of rotor retainer and slide it out of its engagement in the hub. The rotor assembly may then be removed from body. Further disassembly of magazine is not necessary and is prohibited.
(b) Magazine, 20-round.--Slide out floor plate. Hold fingers over bottom of magazine tube to keep magazine spring from flying out. Remove follower.
(c) Butt stock.--Complete disassembly of butt stock is not necessary for ordinary cleaning. However, when necessary for replacement of broken or worn parts, butt stock slide and butt
plate may be removed by taking out the screws holding them in place.
(d) Frame group.--(1) Hold frame in left hand and, using back end of actuator (not knob) as a tool in right hand, do-press short finger of pivot plate and push out rocker pivot with thumb of left hand; lift out rocker and pivot.
(2) Again using actuator but steadying hand with thumb against frame to prevent excessive movement, depress long finger of pivot plate and withdraw safety.
(3) Hold frame upright with grip in right hand. Press simultaneously with both thumbs on sear and trigger pivots. These pivots project sufficiently so that by a quick pressure thereon, pivot plate will protrude on the other side far enough to permit withdrawal. While withdrawing pivot plate with left hand, press down on trigger and sear with thumb of right hand to release pressure of spring on pivots. Do not cant pivot plate during withdrawal. The remaining components of the firing mechanism are then free to be removed. Disconnector can be removed from trigger by simply withdrawing it.
(4) To remove magazine catch, rotate it in a counterclockwise direction to its lull limit and pull out to the left. Removal should be limited to replacement of broken parts. Removal of magazine catch submits magazine catch spring to unnecessary strain and is apt to damage it.
(e) Bolt group.--
(1) Push hammer pin out of bolt from left side; hammer, firing pin, and firing-pin spring will then tend to spring out under the impulse of the firing-pin spring. Caution should be exercised to prevent these parts from springing away and becoming lost. The firing-pin spring must not be stretched.
(2) Extractor should not be removed for ordinary cleaning or disassembling. To do so submits it to unnecessary strain and is apt to cause it to break or become set.
(3) To remove extractor from bolt, insert corner of actuator flange under head of extractor on face of bolt and pull extractor out and up to withdraw it from its groove. When disassembling extractor from or assembling it to bolt, do not lift extractor higher than necessary for lug to clear anchorage hole as otherwise setting or breakage may occur.
(f) Receiver group.--For ordinary training receiver and parts assembled thereto need not be assembled.
(1) To remove rear sight leaf, drive out sight base pin and remove leaf. Take care to see that rear sight leaf plunger and spring do not fly out.
(2) The ejector can be removed by lifting leaf sufficiently to* disengage detent and unscrewing same from receiver. Do not try to unscrew ejector with bolt assembled and in forward position. To do so may damage the ejector and bolt.
(3) Fore grip can be removed by unscrewing fore grip screw-
(4) Barrel should be removed only for purpose of replacement and then only by authorized ordnance personnel.
4. Assembling of groups.--In general, groups and their components are assembled and replaced in the gun in the reverse order of that in which they were removed or disassembled. Certain precautions in assembling ((a) and (b) below) must be observed in order that the parts will function properly after gun is assembled.
(a) In assembling trigger mechanism, first see that magazine catch is in place. Assemble springs in their proper recesses. Assemble disconnector to trigger by depressing disconnector spring and sliding disconnector into place.
(1) Place trigger, trip, sear, and sear lever in their respective positions in frame, making sure forward end of sear lever rests on tip of disconnector. To aline these parts, hold frame in left hand and press downward with end of thumb on trigger and base of thumb on sear. Insert pivot plate. To avoid binding, apply gentle pressure with ball of right hand over entire pivot plate.
(2) Insert safety as far as it will go, and using actuator as a tool depress long finger of pivot plate and push safety home. Turn safety to "fire" position.
(3) Place rocker in position in frame with fiat side against sear lever. Insert rocker pivot as far as it will go. Using actuator as a tool, depress short finger of pivot plate and push rocker pivot home. Turn rocker pivot to "full auto" position. If rocker is assembled backward, the gun will fire full automatic but not semiautomatic.
(b) If extractor has been removed, slide it into place, lifting head only enough to clear stud; avoid excessive pressure. In-
sert firing pin and spring in bolt being careful to avoid stretching firing pin spring. Place hammer in position with rounded edge upward and push hammer pin into place.
5. Replacing groups in gun.--Before replacing groups in gun, be sure ejector is screwed all the way home and that breech oiler is in place.
(a) Place receiver on table or knees, bottom up, and insert actuator in receiver, knob to front. Slide actuator forward and place lock in guideways of receiver, with the word "up" correctly readable from the rear and the arrow pointing toward the muzzle. Slide actuator to the rear and place bolt in position by lowering it into the receiver front end first, moving it to the rear, and allowing it to drop into place.
(b) Slide bolt forward and start recoil spring assembled to buffer guide, into its recess in bolt. Push recoil spring down into bolt until buffer pilot clears end of receiver. Let buffer pilot find its seat in the receiver and snap into place.
(c) For guns equipped with drilled buffer guides, assemble about two-thirds of recoil spring on buffer guide, place retaining pin (nail or strong wire) through coil of spring and hole of buffer guide to hold compressed spring on buffer guide. Care should be taken to see that retaining pin is entered in the hole in buffer guide from the side opposite to that of the milled off flat portion of the buffer flange. Slide the bolt forward and start the loose end of recoil spring into recess in actuator which rides in the bolt. Feed loose end of spring into its recess until rear end of pilot can be seated in hole in rear end of receiver, care being taken to see that buffer disk is in place before pilot is placed in the hole in receiver. Move bolt rearward until rear end of bolt is brought up against spring retaining pin. Remove retaining pin which permits spring completely to seat itself within the recess. Release bolt.
(d) Before fitting frame to receiver, be sure that safety is set at "fire" position and rocker pivot at "full auto." Slide frame onto receiver. Frame latch will lock frame in position. Holding trigger depressed, operate actuator back and forth several times to test mechanism.
SECTION C. CARE AND CLEANING
1. General.--The attention given to a weapon of this type determines largely whether it will shoot accurately and function properly. The bore and chamber must be kept in perfect condition for accurate shooting. Also, it is just as important that the receiver and moving parts be kept clean, lubricated, and in perfect condition for efficient functioning. Care and cleaning; will include the magazines, which must be kept free from rust, grit, gum, etc., in order to function property. When not on the person, the submachine gun should be habitually transported in a suitable boot provided with the necessary brackets for attachment.
2. Cleaning and lubrication--General.--(a) Keep the gun well cleaned and oiled. After each day's firing, clean the bore, chamber, and all parts and surfaces of the receiver, bolt ejector, and extractor that have been in contact with powder gases. Remove frame from receiver and take bolt out; thoroughly clean front end of bolt and extractor. With the bolt removed, the bolt well, the head of the receiver, and the ejector head are readily accessible.
(b) Bore.--(1) As the barrel of the submachine gun is not removed for cleaning, it must be cleaned from the muzzle if the submachine gun cleaning rod is used. However, by using the rifle cleaning rod the barrel can be cleaned from the breech. Push rifle cleaning rod through buffer pilot in back of receiver and thread a patch through eye of rod.
CAUTION.--In cleaning bore, care must be taken not to foul cleaning patch in slots of recoil compensator.
(2) Run several wet patches through bore. For this purpose water must be used; warm water is good, and warm soapy water is better. Remove patch, attach cleaning brush, and run brush back and forth through bore several times. Care should be used to insure that brush goes all the way through bore before direction is reversed. Remove brush and run several wet patches through bore. Follow this by dry patches until patches
come out clean and dry, then saturate a patch in sperm oil and push it through bore.
NOTE.--Sperm oil (U. S. A. Spec. 2-45A) should be used when available. When not available, motor oil, weight 20, or any light grade machine oil may be used in an emergency.
(c) Chamber.--The chamber should be cleaned with the chamber cleaning brush at reasonable intervals in extended firing to facilitate extraction of cartridge cases and to prevent pitting and rusting. It is not necessary to disassemble gun for this purpose. The brush is introduced through ejection opening in receiver and should be vigorously used. Upon completion of firing, the brush having been used the chamber is further cleaned and oiled in the process of cleaning the bore.
(d) Exterior surfaces.--Wipe off exterior surfaces of gun with a dry cloth to remove dampness, dirt, and perspiration, then wipe off all metal surfaces with an oiled (sperm oil) rag. The stock and grips should be wiped with raw linseed oil.
(e) Magazines.--It is imperative that magazines be given the best of care and kept in perfect condition. They should be disassembled, wiped clean and dry, and thinly coated with oil. Dirt that gets into them through careless handling during range or other firing must be removed. Care must be exercised in handling magazine to avoid denting or bending, especially the lips of the mouth of the box type magazines.
(f) Lubricating the gun.---To function efficiently, the gun must be properly lubricated. For this purpose use aircraft machine gun lubricating oil (U. S. A. Spec. 2-27) or sperm oil (U. S. A. Spec. 2-45A) .
(1) Having removed frame from receiver, oil should be dropped over pivot points of trigger and trip, sear and sear lever, and disconnector and rocker.
(2) Holding receiver in left hand, open side up, bolt should be slightly drawn back and oil dropped on locking lugs of lock, on sides of lock, and on all sliding surfaces of bolt and receiver.
(3) Felt pads in breech oiler should be kept well saturated with oil.
(4) After assembling frame to receiver, bolt should be drawn back and a little oil should be dropped on rounded front end of
bolt. Actuator knob should be worked back and forth several times to insure penetration of oil to all parts of mechanism.
(5) All sliding surfaces should be oiled frequently and freely to insure perfect functioning of the gun.
SECTION D. FUNCTIONING
1. General.--The pressure of the gases generated in the barrel by the explosion of the powder in the cartridge is exerted in a forward direction against the bullet, driving it through the bore, and in a rearward direction against the face of the bolt. This force drives the bolt and the actuator together to the rear against the pressure of the recoil spring. During rearward movement, the process of unlocking, extracting, ejecting empty shell, and compressing the recoil spring are affected; during the forward movement, the processes of feeding, locking, and firing the cartridge are accomplished. To simplify explanation of functioning, the cycle has been divided into three phases as set forth below.
2. Backward movement of recoiling parts (first phase).-- The cartridge having been fired, the pressure from the exploding cartridge is transmitted through the forward and of the bolt to the lock to the locking surfaces of the receiver. The powder used is fast burning, so that the highest pressure obtained is nearly instantaneous. The lock being made of bronze and the bolt and receiver being made of steel, the high chamber pressure causes the lock to adhere to the locking surface on the receiver, thus locking the bolt in its forward position until this pressure subsides. As soon as the high chamber pressure has subsided, the lock moves upward, clears the locking surfaces in the receiver, and the bolt can move to the rear. The angle of the lock is such that the moment the lock is moved to clear the receiver locking surfaces there is only sufficient powder in the chamber to force the cartridge case and bolt to the rear, eject the empty case and compress the recoil spring, which thus stores up energy for the forward movement. The empty case is unseated by the chamber pressure as the bolt is unlocked. As soon as the bolt moves back from the abutment on the under side of the receiver, the firing pin spring forces the firing pin to
the rear away from the face of the bolt. The empty cartridge is held on the face of the bolt by the extractor. After the bolt has traveled to the rear about 2 inches the ejector, which protrudes in a groove on the left side of the bolt, comes in contact with the base of the empty cartridge and throws it to the right through the ejection opening. The bolt still has about 1 3/4 inches to go to the rear before the back of the bolt comes in contact with the buffer. The rearward movement of the bolt, carrying the actuator and compressing the recoil spring, expends nearly all the energy imparted by the chamber pressure, so that the bolt does not strike heavily against the buffer. The buffer pad absorbs the remaining shock. On the under side of the bolt there are two sear notches so that, if the bolt strikes the buffer pad, the rear sear notch will pass over the sear and allow the sear to engage in the front notch. If the movement is not strong enough to cause the bolt to strike the buffer pad, the sear will engage in the rear notch. If the bolt moves to the rear far enough to eject the empty cartridge case and to feed the next cartridge from the top of the magazine, the bolt will normally be back far enough to engage the sear with the rear notch.
3. Forward movement of recoiling parts (second phase).-- When the trigger is pulled, the bolt moves forward under the action of the recoil spring, carrying the lock and actuator with it. After the bolt moves forward about 1 inch, the forward end of the bolt comes in contact with the back of a cartridge and pushes it forward until the nose of the bullet comes in contact with the bullet ramp in front of the receiver. The lips of the magazine hold the cartridge in a straight line until the cartridge has almost cleared the magazine. The cartridge is guided into the chamber by the bullet ramp and the lips of the magazine. When the cartridge has been seated in the chamber, the extractor snaps around the rim of the cartridge. Just before the bolt reaches its forward position, the lock is cammed down into the locking grooves in the receiver so that the bolt is completely locked as the hammer on the under side of the bolt strikes the receiver. The hammer being of a triangular shape, the lower point strikes the receiver, causing the hammer to pivot around the hammer pin and strike the head of the firing pin with the upper point, thereby firing the cartridge. The rectangular surface of the
bolt, striking the abutment of the receiver, stops the forward movement.
4. Action of trigger mechanism (third phase).--(a) (1) Rocker pivot set at "single."--When the trigger is pulled, the trigger rotates around the trigger pivot (the forward pin of the pivot plate) and lifts the disconnector up under the sear lever. The sear lever lifts the front end of the sear; this causes the sear to rotate around the sear pivot (the rear pin of the pivot plate), and in so doing depresses the nose of the sear, disengaging it from the sear notch on the under side of the bolt. As the bolt goes forward, the point of the rocker is in the T-groove on the under side of the bolt. When the point of the rocker strikes the rear end of the T-groove, the rocker is forced forward. The rounded part of the rocker comes in contact with the disconnector and forces the disconnector out from under the sear lever. As soon as the disconnector has been disengaged from the sear lever, the sear spring and the sear lever spring force the sear and sear lever up into firing position, so that the sear notch on the bolt will catch on the next rearward movement of the bolt.
(2) Rocker pivot set at "full auto."--The rocker pivot is of eccentric design so that when the rocker pivot is set at "full auto" the rocker is lowered enough to allow the bolt to move forward without striking the point of the rocker. Therefore, the sear remains in its lowered position as long as the trigger is depressed. The rocker pivot cannot be turned from "full auto" to "single" unless bolt is retracted.
(b) (1) Safety set at "fire."--When the safety is turned toward the front, the flat-milled surface is in such a position that the sear is allowed to rotate around the sear pivot.
(2) Safety set at "safe."--When the safety is turned toward the rear, the rounded part of the safety engages in a groove in the rear of the sear and locks the sear in its uppermost position. The safety can be turned only when the bolt is to the rear.
(c) The magazine catch rotates around its pin and is held down in the engaged position by the magazine catch spring. The stud on the magazine catch is to hold the box-type magazine; the drum type is held by the rectangular catch on the left side. The trip functions only when the box-type magazine is used. As the magazine empties, a fin on the back of the magazine
follower rises up under the trip, causing the trip to rotate around the trigger pin, compressing the disconnector spring holding the disconnector forward of the sear lever. Thus the bolt will not go forward on an empty chamber when the box magazine is used.
SECTION E. STOPPAGES AND IMMEDIATE ACTION
1. Misfire.--In the event of misfire, retract or cock bolt with a sharp, quick pull on actuator knob. This should insure ejection of misfired cartridge. Inspect chamber to see that it does not contain an unexpended round.
2. Other stoppages.--For any other malfunction, retract bolt as above and clear throat and chamber of gun by turning gun over on its side and letting case or cartridge roll out. If necessary, remove magazine and allow cartridge or case to fall out the bottom. While manipulating the gun under those circumstances, always set the gun at "safe."
SECTION F. SPARE PARTS AND ACCESSORIES
1. Spare parts.--The parts of any submachine gun will in time become unservicable through breakage or wear resulting from continuous usage. For this reason spare parts are provided for replacement of the part's most likely to fail, for use in making minor repairs, and in general upkeep of the submachine gun. Sets of spare parts should be maintained as complete as possible at all times and should be kept clean and lightly oiled to prevent rust. Whenever a spare part is used to replace a defective part, the defective part should be repaired or a new one substituted in the spare parts set. Parts that are carried complete should at all times be correctly assembled and ready for immediate insertion in the submachine gun.
Twenty- or fifty-round magazines are also issued as spares; the former for use with submachine guns issued for use by cavalry motorcyclists and the latter for submachine guns issued for use by cavalry combat vehicle troops. The quantity of magazines issued per gun is based on the allowance of ammunition authorized.
The allowances of spare parts and of magazines are prescribed in SNL A-32.
2. (a) General.--Accessories include the tools required for disassembling and assembling and for the cleaning and preservation of the gun. They must not be used for any purpose, other than as prescribed. There are a number of accessories, the names or general chacteristics of which indicate their uses or applications. Therefore, detailed description or method of use of such items is not outlined herein. However, accessories-embodying special features or having special uses are described in 6 below.
(b) (1) Brush, chamber cleaning, M6.--The brush consists of a steel wire core with bristles, the core being twisted in a spiral to hold the bristles in place. It is used to clean the chamber of the submachine guns.
(2) Brush, cleaning, caliber .45, MB.---The brush consists of a brass wire core with bristles and tip. The core is twisted in a spiral and holds the bronze bristles in place. The brass tip which is threaded for attaching the brush to the cleaning rod is soldered to the end of the core.
(3) Case, accessory and spare parts, M1918.--This is a leather box-shaped case, approximately 2 1/4 inches wide, 3 1/2 inches high, and 5 1/2 inches long. It is used to carry spare parts and a number of the smaller accessories.
(4) Rod, cleaning, submachine gun.--This consists of a long steel rod having a circular loop at one end and a cleaning patch slot at the other end. Permanently affixed to the cleaning patch end of the rod is a head having a threaded hole to receive the cleaning brush, caliber .45, M5.
(5) Sling, gun, M1923 (webbing).--The gun sling is fastened to the swivels provided on the gun. It consists of a long and short strap, either of which may be lengthened or shortened as desired to suit the particular man using it.
(b) Thong.--The thong consists of a tip with cleaning patch slot and a weight tied to the ends of a 30-inch length of cord. It is used in cleaning the bore of the submachine gun.
SECTION G. INDIVIDUAL SAFETY PRECAUTIONS
(a) Before firing--
- Test trigger mechanism as "safe" and "single."
- See that bore is clear and clean.
- Work bolt back and forth rapidly several times to see that it is clean, well-oiled, and works freely.
- Examine magazines and eliminate faulty ones.
- See that each magazine is free from dirt and that it is properly loaded.
(b) Insert loaded magazine only on order of the commanding officer. Do not attach loaded magazine until ready to fire.
(c) Carry gun with bolt retracted and safety on "safe" until ordered to attach magazine, and keep safety on "safe" until gun is raised to fire.
(d) Keep the trigger finger outside trigger guard until gun is raised to fire.
(e) From time magazine is attached until gun is cleared and clearance checked, keep gun pointed toward target.
(f) For semiautomatic fire make certain that rocker pivot is set on "single" and the safety on "safe" before attaching magazine.
(g) For full automatic fire, make certain that rocker pivot is set on "full auto" and the safety on "safe" before attaching magazine.
(h) Habitually set the safety at "safe" while changing magazines and during lulls in firing.
(l) To clear gun, first remove magazine.
(j) At CEASE FIRING set the safety at "safe," remove magazine, and see that no cartridge remains in the chamber before turning away from the target.
(k) After gun has been cleared and checked for clearance, close the bolt on an empty chamber.
Chapter 4. MAGAZINE, RIFLE CALIBER .30, MODEL 1903
SECTION A. GENERAL
1. The Navy, which requires a small number of rifles compared with Army, uses in general the same type of rifle and ammunition as the Army and obtains this material from the War Department. This is in order to provide for interchangeability of material and to facilitate the supply.
2. Practically all military rifles in use at the present time have the same general features. They are bolt action magazine rifles of approximately .30 caliber fitted with knife bayonet, equipped with open sight for battle use, and weigh approximately 9 pounds. The bolt must be opened by hand, and the trigger must be pulled for each shot. The ammunition is usually furnished in clips and the magazine of the rifle holds one full clip.
The military rifle must be free from complications, ruggedly constructed, and capable of standing rough usage. Such refinements as telescopes sights, etc., cannot be used on rifles which are issued for general service.
3. The United States Army and Navy are equipped with the United States rifle caliber .30, model 1903. This rifle is usually referred to in the service as the Springfield rifle. The following are the essential features of this rifle:
Weight, 9 pounds.
Weight of bayonet, 1 pound.
Weight of bullet, 172 grains.
Muzzle velocity, 2,700 feet per second.
Maximum powder pressure in chamber, 51,000 pounds.
Length of travel of bullet in bore, 21.70 inches.
Number of grooves in rifling, 4.
Twist of rifling, right hand, uniform 1 turn in 10 inches.
Sight radius, 22.12 inches.
Trigger pull, 4.25 to 5.5 pounds.
Maximum range at 45° elevation, about 5,500 yards.
Mechanical Operation of the Rifle
1. Assembled parts and their operation.--Most of the operating parts may be included under the bolt mechanism and the magazine mechanism.
2. (a) The bolt mechanism consists of the bolt, sleeve, sleeve lock, extractor, extractor collar, safety lock, firing pin, firing-pin sleeve, striker, and mainspring.
(b) The bolt moves backward and forward and rotates in the well of the receiver; it carries a cartridge, either from the magazine or one placed by hand in front of it, into the chamber and supports its head when fired.
(c) The sleeve unites the parts of the bolt mechanism, and its rotation with the bolt is prevented by the lugs on its sides coming in contact with the receiver.
(d) The hook of the extractor engages in the groove of the cartridge case and retains the head of the. latter in the countersink of the bolt until the case is ejected.
(e) The safety lock, when turned to the left, is inoperative; when turned to the right--which can only be done when the piece is cocked---the point of the spindle enters its notch in the bolt and locks the bolt; at the same time its cam forces the cocking piece slightly to the rear, out of contact with the sear, and locks the firing pin.
3. (a) The bolt mechanism operates as follows: To open the bolt, raise the handle until it comes in contact with the left side of the receiver and pull directly to the rear until the top locking lug strikes the cut-off.
(b) Raising the handle rotates the bolt and separates the locking lugs from their locking shoulders in the receiver, with which they have been brought into close contact by the powder pressure. This rotation causes the cocking cam of the bolt to force the firing pin to the rear, drawing the point of the striker into the bolt, rotation of the firing pin being prevented by the lug on the cocking piece projecting through the slot in the sleeve into its groove in the receiver. As the sleeve remains longitudinally stationary with reference to the bolt, this rearward motion of the firing pin, and consequently of the striker, will start the compression of the mainspring, since the rear end of the latter
bears against the front end of the barrel of the sleeve and its front end against the rear end of the firing-pin sleeve.
(c) When the bolt handle strikes the receiver, the locking lugs have been disengaged, the firing pin has been forced to the rear until the sear notch of the cocking piece has passed the sear nose, the cocking piece nose has entered the cock notch in the rear end of the bolt, the sleeve lock has engaged its notch in the bolt, and the mainspring has been almost entirely compressed.
(d) During the rotation of the bolt a rear motion has been imparted to it by its extracting cam coming in contact with the extracting cam of the receiver, so that the cartridge case will be started from the chamber.
The bolt is then drawn directly to the rear, the parts being retained in position by the cocking piece nose remaining in the cock notch and locked by the sleeve lock engaging its notch in the bolt.
(e) To close the bolt, push the handle forward until the extracting cam on the bolt bears against the extracting cam on the receiver, thereby unlocking the sleeve from the bolt, and turn the handle down. As the handle is turned down the cams of the locking lugs bear against the locking shoulders in the receiver, and the bolt is forced slightly forward into its closed position. As all movement of the firing pin is prevented by the sear nose engaging the sear notch of the cocking piece, this forward movement of the bolt completes the compression of the mainspring, seats the cartridge in the chamber, and, in single loading, forces the hook of the extractor into the groove of the cartridge case. In loading from the magazine the hook of the extractor, rounded at its lower edge, engages in the groove of the top cartridge as it rises from the magazine under the action of the follower and magazine spring. The piece is then ready to fire.
4. (a) To pull the trigger, the finger piece must be drawn to the rear until contact with the receiver is transferred from its bearing to the heel, which gives a creep to the trigger, and then until the sear nose is withdrawn from in front of the cocking piece.
(b) Just before the bolt is drawn fully to the rear, the top locking lug strikes the heel of the ejector, throwing its point suddenly to the right in the lug slot. As the bolt moves fully to the rear, the rear face of the cartridge case strikes against
the ejector point and the case is ejected, slightly upward and to the right, from the receiver,
(c) Double loading from the magazine is prevented by the extractor engaging the cartridge ease as soon as it rises from the magazine and holding its head against the face of the bolt until ejected.
(d) It will be noted that in this system of bolt mechanism the compression of the mainspring, the seating of the cartridge in, and starting of the empty case from the chamber are done entirely by the action of the cams.
(e) The piece may be cocked either by raising the bolt handle until it strikes the left side of the receiver and then immediately turning it down or by pulling the cocking piece directly to the rear.
(f) In firing, unless the bolt handle is turned fully down, the cam on the cocking piece will strike the cocking cam on the bolt and the energy of the mainspring will be expended in closing the bolt instead of on the primer; this prevents the possibility of a cartridge being fired until the bolt is fully closed. The opening and closing of the bolt should each be done by one continuous motion.
5. The magazine mechanism includes the floor plate, follower, magazine spring, and cut-off.
(a) To charge the magazine, see that the cut-off is turned up, showing "On," draw the bolt fully to the rear, insert the cartridges from a clip, or from the hand, and close the bolt. To charge the magazine from a clip, place either end of a loaded clip in its seat in the receiver and with the thumb of the right hand press the cartridges down into the magazine until the top cartridge is caught by the right edge of the receiver. The cartridge ramp guides the bullet and cartridge case into the chamber. The magazine can be filled, if partly filled, by inserting cartridges one by one. Pushing the bolt forward, after charging the magazine, ejects the clip.
(b) When the cut-off is turned down, the magazine is "off". The bolt cannot be drawn fully back, and its front end projecting over the rear end of the upper cartridge holds it down in the magazine below the action of the bolt. The magazine mechanism then remains inoperative, and the arm can be used as a single loader, the cartridges in the magazine being held in
reserve. The arm can readily be used as a single loader with the magazine empty.
(c) When the cut-off is turned up, the magazine is "on." The bolt can be drawn fully to the rear, permitting the top cartridge to rise high enough to be caught by the bolt in its forward movement. As the bolt is closed this cartridge is pushed forward into the chamber, being held up during its passage by the pressure of those below. The last one in the magazine is held up by the follower, the rib on which directs it into the chamber.
(d) In magazine fire, after the last cartridge has been fired and the bolt drawn fully to the rear, the follower rises and holds the bolt open to show that the magazine is empty.
SECTION B. PRECAUTIONS
1. If it is desired to carry the piece cocked, with a cartridge in the chamber, the bolt mechanism should be secured by turning the safety lock to the right. Under no circumstances should the firing pin be let down by hand on a cartridge in the chamber.
2. To obtain positive ejection, and to insure the bolt catching the top cartridge in magazine, when loading from the magazine, the bolt must be drawn fully to the rear in opening it.
3. When the bolt is closed, or slightly forward, the cut-off may be turned up or down as desired. When the bolt is in its rearmost position to pass from loading from the magazine to single loading it is necessary to force the top cartridge or follower below the reach of the bolt, to push the bolt slightly forward, and to turn the cut-off down, showing "Off."
4. In case of a misfire it is unsafe to draw back the bolt immediately, as it may be a case of hangfire. In such cases the piece should be cocked by drawing back the cocking piece.
5. It is essential for the proper working and preservation of all cams that they be kept lubricated.
6. Never fire the rifle with grease or any obstruction in the bore whether near the breech or the muzzle. Practically all cases of burst barrels can be traced to some obstruction left in the bore, such as a cleaning patch, mud, or the like.
(A) Dismounting and Assembling
1. The bolt and magazine mechanism can be dismounted without removing the stock. The latter should never be done, except for making repairs, and then only by some selected and instructed man.
2. (a) To dismount bolt mechanism, place the cut-off at the center notch, cock the arm and turn the safety lock to a vertical position, raise the bolt handle and draw out the bolt.
(b) Hold bolt in left hand, press sleeve lock in with thumb of right hand to unlock sleeve from bolt, and unscrew sleeve by turning to the left.
(c) Hold sleeve between forefinger and thumb of the left hand, draw cocking piece back with middle finger and thumb of right hand, turn safety lock down to the left with the forefinger of the right hand in order to allow the cocking piece to move forward in sleeve and thus partially relieving the tension of mainspring; with the cocking piece against the breast, draw back the firing-pin sleeve with the forefinger and thumb of right hand and hold it in this position while removing the striker with the left hand, remove firing pin sleeve and mainspring, pull firing pin out of sleeve, turn the extractor to the right, forcing its tongue out of its groove in the front of the bolt, and force the extractor forward and off the bolt.
(d) To assemble bolt mechanism, grasp with the left hand the rear of the bolt, handle up, and turn the extractor collar with the thumb and forefinger of the right hand until its lug is on a line with the safety lug on the bolt; take the extractor in the right hand and insert the lug on the collar in the undercuts in the extractor by pushing the extractor to rear until its tongue comes in contact with the rim on the face of the bolt (a slight pressure with the left thumb on the top of the rear part of the extractor assists in this operation) ; turn the extractor to the right until it is over the right lug; take the bolt in the right hand and press the hook of the extractor against the butt plate or some rigid object, until the tongue on the extractor enters its groove in the bolt.
(e) With the safety lock turned down to the left to permit the firing pin to enter the sleeve as far as possible, assemble the sleeve
and firing pin; place the cocking piece against the breast and put on mainspring, firing-pin sleeve, and striker. Hold the cocking piece between the thumb and forefinger of the left hand, and pressing the striker point against some substance, not hard enough to injure it, force the cocking piece back until the safety lock can be turned to the vertical position with the right hand; insert the firing pin in the bolt and screw up the sleeve (by turning it to the right) until the sleeve lock enters its notch on the bolt.
(f) See that the cut-off is at the center notch; hold the piece under floor plate in the fingers of the left hand, the thumb extending over the left side of the receiver; take bolt in right hand with safety lock in a vertical position and safety lug up; press rear end of follower down with left thumb and push bolt into the receiver, lower bolt handle; turn safety lock and cut-off down to the left with right hand.
3. (a) To dismount magazine mechanism.--With the bullet end of a cartridge press on the floor plate catch (through the hole in the floor plate), at the same time drawing the bullet to the rear; this releases the floor plate.
(b) Raise the rear end of the first limb of the magazine spring high enough to clear the lug on the floor plate and draw it out of its mortise; proceed in the same manner to remove the follower.
(c) To assemble magazine spring and follower to floor plate, reverse operation of dismounting. Insert the follower and magazine spring in the magazine, place the tenon on the front end of the floor plate in its recess in the magazine, then place the lug on the rear end of the floor plate in its slot in the guard, and press the rear end of the floor plate forward and inward at the same time, forcing the floor plate into its seat in the guard.
4. Complete dismounting.--The bolt and magazine mechanism having been dismounted, proceed as follows:
(a) Turn safety lock to dismounting bevel on sleeve and remove it by striking the thumbpiece a light blow.
(b) To dismount the sleeve lock, drive out sleeve lock pin from the top and remove lock and spring, being careful not to lose the spring.
(c) Remove front sight pin and remove front sight.
(d) Press in rear end of lower band spring and drive forward the lower band by a few sharp blows on the lug and then on top with a hardwood block.
(e) Remove upper band screw and drive upper band forward, in the same manner prescribed for the lower band.
(f) Move upper band forward on barrel until stopped by movable stud, and then remove lower band, by slipping it over upper band and movable stud. To remove upper band entirely from barrel requires the removal of the front sight screw and the movable stud.
(g) Draw hand guard forward until free from the fixed base and remove.
(h) Remove guard screws and guard. It may be necessary to tap gently on the front and rear of the guard bow to loosen.
(i) Remove barrel and receiver from stock.
(j) To remove the lower band spring, drive its spindle out of its hole in the stock from the left.
(k) Unscrew the butt swivel, consisting of the plate, swivel, and pin, permanently assembled, which is issued complete.
(l) Unscrew butt-plate screws and remove butt plate from stock.
(m) Unscrew butt-plate spring screw and remove the butt plate; spring; drive out butt-plate pin and remove butt plate cap.
(n) Remove cut-off by loosening the screw in the end of the thumbpiece until it disengages the groove in the cut-off spindle; insert the blade of a screw driver in the notch in the rear end of the spindle and force it out. Remove the spring and tho plunger, being careful not to lose them.
(o) Remove the ejector by driving out the ejector pin from tho upper side.
(p) Remove sear and trigger by driving out the sear pin from the right, being careful not to lose the sear spring.
(q) Remove trigger from sear by driving out the trigger pin from either side.
(r) Remove floor-plate catch and spring by driving out tho pin from either side.
(s) Remove bolt stop by inserting a small punch or end of striker in the hole in the left end and forcing it from its pocket.
The leaf should never be removed from the movable base except for the purpose of making repairs.
The fixed base and the fixed stud should never be removed from the barrel.
(B) Assembling the Rifle
1. Reverse and follow in inverse order the operations of dismounting. In assembling the sleeve lock to the sleeve, be careful to compress the lock and spring while drh ing in the pin from the bottom of the sleeve.
2. To assemble the safety lock and sleeve, insert the safety-lock spindle in its hole in the sleeve as far as it will go; then, with the thumbpiece vertical and pressed against some rigid object, introduce the point of the tool provided for this purpose between the safety-lock spindle and the safety-lock plunger, forcing the latter into the thumbpiece until it slips over the edge of the sleeve. Further pressure on the safety-lock thumbpiece, together with the gradual withdrawal of the tool, will complete the assembling.
3. The floor-plate spring and the cut-off spring are alike, except in length. The latter being the longer, care should be taken not to substitute one for the other.
SECTION D. CARE OF THE RIFLE
1. The proper care of the bore requires conscientious, careful work, but it pays well in reduced labor of cleaning and in prolonged accuracy, life of the barrel, and better results in target practice. Briefly stated, the care of the bore consists of removing the fouling resulting from firing to obtain a chemically clean surface, and coating this surface with a film of oil to prevent rusting. The fouling, which results from firing, is of two kinds-- one, the products of combustion of the powder and primer composition; two, cupro-nickel scraped off (under the abrading action of irregularities or grit in the bore.) The former, because of its acid reaction, is highly corrosive; that is, it will induce rust and must be removed. Metal fouling of itself is inactive, but may cover powder fouling and prevent the action of cleaning agents
until removed, and when accumulated in noticeable quantities it reduces the accuracy of the rifle.
2. Methods of removing powder fouling.--The best method to remove powder fouling is by the use of boiling or hot water, if obtainable, and in the absence of hot water, cold water should be used. The barrel should be washed out five or six times by pouring a cupful at each washing through the barrel with a funnel. After washing, a bristle brush should be run through the barrel several times and then the bore should be dried out by running dry flannel patches through it. After it is thoroughly dry, it should be oiled with sperm oil.
Powder fouling may be readily removed by scrubbing with hot sal soda solution, but this solution has no effect on the metal fouling of cupro-nickel. It is therefore necessary to remove all metal fouling before assurance can be had that all powder fouling has been removed and the bore safely oiled. Normally, after firing a barrel in good condition, the metal fouling is so slight as to be hardly perceptible. It is merely a smear of infinitesimal thickness, easily removed by solvents of cupro-nickel. However, due to pitting, the presence of dust, other abrasives, or accumulation, metal fouling may occur in clearly visible flakes or patches of much greater thickness and much more difficult to remove.
In cleaning the bore after firing, it is well to proceed as follows: Swab out the bore with sal soda solution (see below) to remove powder fouling. A convenient method is to insert the muzzle of the rifle into the can containing the sal soda solution and, with the cleaning rod inserted from the breech, pump the barrel full a few times. Remove and dry with a couple of patches. Examine the bore to see that there are in evidence no patches of metal fouling which, if present, can be readily detected by the naked eye, then swab out with the swabbing solution, a. dilute metal-fouling solution. (See below.) The amount of swabbing required with the swabbing solution can be determined only by experience, assisted by the color of the patches. Swabbing should be continued, however, as long as the wiping patch-is discolored by a bluish-green stain. Normally a couple of minutes' work is sufficient. Dry thoroughly and oil.
3. To oil the barrel.--The proper method of oiling the barrel is as follows: Wipe the cleaning rod dry; select a clean, patch
and thoroughly saturate it with sperm oil; scrub the bore with the patch, finally drawing the patch smoothly from the muzzle to the breech, allowing the cleaning rod to turn with the rifling. The bore will be found now to be smooth and bright, so that any subsequent rust and sweating can be easily detected by inspection.
4. Methods of removing metal fouling.--If the patches of metal fouling are seen upon visual inspection of the bore, the standard metal-fouling solution prepared as hereinafter prescribed must be used. After scrubbing out with the sal soda solution, plug the bore from the breach with a cork at the front end of the chamber, or where the rifling begins. Slip a 2-inch section of rubber hose over the muzzle down to the sight and fill with the standard solution -to at least one half inch above the muzzle of the barrel. Let it stand for 30 minutes, pour out the solution, remove the hose and breech plug, and swab out thoroughly with sal soda solution to neutralize and remove all trace of ammonia and powder fouling. Wipe the barrel clean and dry; then oil. With few exceptions, one application is sufficient, but if all fouling is not removed as determined by careful visual inspection of the bore and of the wiping patches, repeat as described above.
5. After properly cleaning with one of the solutions, as has just been described, the bore should be clean and safe to oil and put away; but as a measure of safety a patch should always be run through the bore on the next day, and the bore and wiping patch examined to insure that cleaning has been properly accomplished. The bore should then be oiled, as described above.
6. If the solutions are not available, the barrel should be scrubbed, as already described, with the sal soda solution, dried, and oiled with a light oil. At the end of 24 hours it should again be cleaned, when it will usually be found to have "sweated," that is, rust having formed under the smear of metal fouling where powder fouling was present, the surface is puffed up. Usually a second cleaning is sufficient, but to insure safety it should be again examined at the end of a few days before final oiling. The swabbing solution should always be used, if available, for it must be remembered that each puff when the bore "sweats" is an incipient rust pit.
A clean dry surface having been obtained, to prevent rust it is necessary to coat every portion of this surface with a film of neutral oil. If the protection required is but temporary and the arm is to. be cleaned or fired in a few days, a sperm oil may be used. This is easily applied and easily removed, but has not sufficient body to hold its surface for more than a few days. If rifles are to be prepared for storage or shipment, a heavier oil must be used.
(B) Preparing Arms for Storage or Shipment
In preparing arms for storage or shipment they should be cleaned with particular care, using the metal-fouling solution as described above. Care should be taken, insured by careful inspection on succeeding day or days, that the cleaning is properly done and all traces of ammonia solution removed. The bore is then ready to be coated with heavy oil. In order, therefore, to insure that every part of the surface is coated with a film of oil, the heavy oil should be warmed. Apply the heavy oil first with a brush; then, with the breech plugged, fill the barrel to the muzzle, pour out the surplus, remove the plug, and allow to drain. It is believed that more rifles are ruined by improper preparation for storage than from any other cause. If the bore is not clean when oiled; that is, if powder fouling is present or rust has started, a half inch of heavy oil on the outside will not stop its action, and the barrel will be ruined. Remember that the surface must be perfectly cleaned before the heavy oil is applied. If the instructions as given above are carefully followed, arms may be stored for years without harm.
(C) Preparation of Solutions
1. Sal-soda solution.--This should be a saturated solution of sal soda (carbonate of soda). A strength of at least 20 percent is necessary. Soda ash may be substituted for sal soda, in which case it should be borne in mind that 6 ounces of soda ash is equivalent to 1 pound of sal soda.
Sal soda, one-fourth pound, or 4 heaping tablespoonfuls.
Water, 1 pint.
The sal soda will dissolve more readily in hot water.
2. Swabbing solution.--Ammonium persulphate, 60 grains, tablespoonful smoothed off.
Dissolve the ammonia persulphate in the water and add the ammonia. Keep in tightly corked bottle, pouring out only what is necessary at the time.
Ammonia (28 percent), 6 ounces, or 3/8 of a pint, or 12 tablespoonfuls.
Water, 4 ounces, or 1/4 pint, or 8 tablespoonfuls.
3. Standard metal-fouling solution.--Ammonium persulphate 1 ounce or 2 medium-heaping tablespoonfuls.
Ammonium carbonate, 200 grains or 1 heaping table-spoonful.
Ammonia (28 percent), 6 ounces, or 3/8 pint, or 12 tablespoonfuls.
Water, 4 ounces, or 1/4 pint, or 8 tablespoonfuls.
Powder the persulphate and carbonate together, dissolve in the water and add the ammonia; mix thoroughly and allow to stand for 1 hour before using. It should be kept in a strong bottle, tightly corked. The solution should not be used more than twice, and used solution should not be mixed with unused solution, but should be bottled separately. The solution, when mixed, should be used within 30 days. Care should be used in mixing and using this solution to prevent injury to the rifle. The ammonia solution should not be used in a warm barrel. An experienced petty officer should mix the solution and superintend its use.
Neither of these ammonia solutions has any appreciable action on steel when not exposed to the air, but if allowed to evaporate on steel they attack it rapidly. Care should, therefore, be taken that none spills on the mechanism and that the barrel is washed out promptly with soda solution. The first application of soda solution removes the greater portion of the powder fouling and permits a more effective and economical use of the ammonia solution. These ammonia solutions are expensive and should be used economically.
The standard metal-fouling solution is preferred when available.
SECTION E. GENERAL REMARKS
1. It is a fact recognized by all that a highly polished steel surface rusts much less easily than one which is roughened; also that a barrel which is pitted fouls much more rapidly than one which is smooth. Every effort, therefore, should be made to prevent the formation of pits, which are merely enlarged rust spots, and which not only affect the accuracy of the arm but increase the labor of cleaning.
2. The chambers of rifles are frequently neglected because they are not readily inspected. Care should be taken to see that they are cleaned as thoroughly as the bore. A roughened chamber delays greatly the rapidity of fire, and not infrequently causes shells to stick.
3. Rifles should always be cleaned from the breech, thus avoiding possibly injury to the rifling at the muzzle which would affect the shooting adversely. If the bore for a length of 6 inches at the muzzle is perfect, a minor injury near the chamber will have little effect on the accuracy of the rifle. The rifle should be cleaned as soon as conditions permit. The fouling is easier to remove then, and if left longer it will corrode the barrel.
4.If gas escapes at the base of the cartridge, it will probably enter the well of the bolt through the striker hole. In this case the bolt mechanism must be dismounted and the parts and well of the bolt thoroughly cleaned.
5.Before assembling the bolt mechanism, the firing pin, the barrel of the sleeve, the body of striker, the well of the bolt, and all cams should be wiped with an oiled rag.
6.Many of the parts can generally be cleaned with dry rags. All parts after cleaning should be wiped with an oiled rag.
7.The best method of applying oil is to rub with a piece of cotton cloth upon which a few drops of oil have been placed, thereby avoiding the use of an unnecessary amount of oil; this method will, even in the absence of the oiler, serve for .the cams and bearings, which should be kept continually oiled.
8.Any part that may appear to move hard can generally be freed by the use of a little oil.
9.The stock and hand guard may be coated with raw linseed oil and polished by rubbing with the hand.
10.Sperm oil should only be used for lubricating metallic bearing and contact surfaces.
Chapter 5. AUTOMATIC PISTOL, CALIBER .45, MODEL 1911
SECTION A. GENERAL
1. The Navy, which requires a small number of pistols as compared with the Army, uses in general the same type of pistol and ammunition as the Army and obtains this material from that arm of the service. This is in order to provide for interchangeability of material and to facilitate the supply.
2. The United States Army and Navy are equipped with the United States automatic pistol, caliber .45, model 1911. The following are the essential features of this pistol:
Weight, 2 pounds 7 ounces
Trigger pull, 6 to 7 1/2pounds
Total length, 8.593 inches
Length of barrel, 5.025 inches
Diameter of bore, 0.445 inch
Number of grooves, 6
Width of grooves, 0.1522 inch
Depth of grooves, 0.003 inch
Width of lands, 0.072 inch
Twist, left-handed, one turn in 16 inches
Front sight above axis of bore, 0.5597 inch
Maximum range, 45° elevation, 1,955 yards.
SECTION B. DETAILED DESCRIPTION
1. The three principal parts of the pistol are the receiver, barrel, and slide.
2. (a) The receiver has suitable guides for the reciprocating slide, and a hollow handle in which the magazine is inserted from below and locked in place by the magazine catch. The magazine may be removed by pressure upon the checkered end of the magazine catch which projects from the left side of the receiver in a convenient position for operation by the thumb.
Figure 20.--.45 cal. Automatic pistol.
(b) The magazine catch engages with and locks the magazine under the pressure of the magazine catch spring and is held in the receiver by means of the magazine catch lock.
(c) The magazine consists of a magazine tube closed at the bottom by means of the magazine base secured with two magazine pins. The magazine base has riveted to it the magazine loop, to which the magazine tube is contained the magazine spring, exerting a pressure against the magazine follower which serves as a movable platform for the cartridges.
(d) Secured at each end of the handle of receiver on both sides are screw bushings, onto which are fitted the stocks and into which, to secure the latter, are screwed the stock screws.
(e) In front of the handle of receiver, in the trigger guard, is seated the trigger; in rear and above the handle the firing mechanism is arranged, comprising the hammer mounted on the hammer pin, the sear and (automatic) disconnector mounted together on the sear pin, the grip safety, and safety lock; also the mainspring and the sear spring. The mainspring is seated within the mainspring housing and there held by the mainspring-cap pin. The mainspring housing also contains the mainspring cap and the housing-pin retainer. The conical point of the latter protrudes slightly into the hole for the housing pin, engaging with the groove around the middle thereof, thereby holding the housing pin in place. Into the base of the mainspring housing is fitted the lanyard loop secured by the lanyard-loop pin.
(f) The sear spring has a rib on its lower end which fits into a slot in the rear wall of the magazine seat and keeps the spring from moving vertically. The mainspring housing, bearing against the rear of the spring, locks it in position and gives to it the required tension. The hammer strut is attached to the hammer in rear of its pivot by means of the hammer-strut pin. Its lower end rests in the mainspring cap.
(g) Above the handle on the left side are the slide stop plunger and safety-lock plunger, with their ends protruding from the front and rear, respectively, of the plunger tube. The plunger spring is seated between the plungers within the plunger tube and yieldingly holds them in position.
(h) The ejector is seated at the top of the receiver near the rear end, at the left side. It is held in place by the ejector pin.
(i) The top of the receiver forward of the trigger guard has a semitubular extension which forms the seat for the rear portion of the recoil spring.
3. (a) The barrel of the pistol is largest at the breech, and at the top has two transverse locking ribs, the forward edges of which, together with the forward edge of the breech portion, serve to positively interlock the barrel with the slide when in the firing position. At its rear is an extension which facilitates the entrance of the cartridge from the magazine into the chamber. The rear end of the barrel is attached to the receiver by the link, link pin, and the pin of the slide stop, and, swinging thereon, can move a limited distance lengthwise and also in a vertical plane.
(b) The side walls of the slide overlap the sides of the receiver, and being provided with longitudinal ribs corresponding with similar grooves at the top of the receiver, the slide is free to move longitudinally.
4. (a) The slide has at its front end a strong tubular abutment which is in line with the forward portion of the receiver, and which permits the slide to move to the rear until the rear end of the abutment comes in contact with the flange of the recoil-spring guide against the shoulder in the receiver at its forward end, thereby positively limiting the rearward movement of the slide. Therefore the latter necessarily is assembled to. the receiver from the front, and is prevented from being thrown rearward from the receiver under any circumstances.
(b) In the abutment at the front end of the slide is seated the forward end of the recoil spring fitted into the plug. The rear end of the recoil spring fitted onto the recoil-spring guide, rests against the shoulder in the front end of the receiver.
(c) On the top of slide are mounted the front sight and rear sight.
(d) The barrel bushing fits into the front end of the slide, supports the muzzle end of the barrel, and holds the plug and recoil spring in place.
(e) When the slide and the barrel therein are mounted upon the receiver and the slide stop is in its place, so that the pin part of the slide stop locks the barrel to the receiver through the link, the slide is thereby positively locked in place upon the receiver.
(f) The firing pin, firing-pin spring, and (shell) extractor are carried in the rear end of the slide and locked by the firing-pin
spring. By pressing the firing pin forward so as to clear the firing-pin stop, the latter is released and may be removed downwardly, leaving both firing pin and extractor free for removal.
(g) The slide stop consists of the pin part, which serves as a pivot and passes through the link, and a body, on which is a thumb piece, for releasing the slide from the open position. 5. (a) The safety lock consists of a thin plate, a projecting pin, a thumbpiece, and a projecting stud. The pin part serves as a pivot for the safety lock and is at the same time a pivot for the grip safety. The upper corner of the plate has an angle which will fit into a correspondingly shaped recess in the slide. When the slide is in this forward position and the hammer is cocked, the safety lock may be pushed up manually by means of the thumbpiece, thereby positively locking the hammer and the slide. While the safety lock is being pushed up into the locking position the stud on the safety lock is being carried upward, and it finally stands in rear of the lower arm of the sear blocking the sear and causing the locking of the hammer. If the safety lock is pressed down so as to release the slide, the projecting stud of the safety lock clears the sear, permitting the sear to be operated by the trigger thereby causing the release of the hammer if the grip safety is pressed inward, as by the hand grasping the handle of the pistol, and the trigger is pulled.
(b) The grip safety is pivoted in the upper part of the receiver. Its lower part projects from the rear face of the handle under pressure of the short leaf of the sear spring, thereby locking the trigger whenever the handle of the pistol is released. But when the handle is grasped, as in the firing position, the grip safety releases the trigger without requiring the attention or thought of the firer.
(c) The (automatic) disconnector is mounted in the receiver at the rear of the magazine seat. In the under side of the slide and near its rear and a recess is provided which stands above the top of the disconnector when the slide is in the forward firing position. With the slide in this position the disconnector is raised to its operative position by the center leaf of the sear spring, and it then will transmit the movement of the trigger to the sear. The forward surfaces of the recess of the slide and of the projecting end of the disconnector are inclining, so that the rearward movement of the slide depresses the connector until the slide again
returns to its forward position. In this depressed position of the •disconnector the trigger is disconnected from the sear, allowing the sear to reengage the hammer. This arrangement automatically and positively prevents firing of the pistol except when all its parts are in the fully closed and locked firing position, and it also prevents more than one shot from following each pull of the trigger.
SECTION C. TO DISMOUNT AND ASSEMBLE THE PISTOL
1. Remove the magazine by pressing the magazine catch.
2. Press the plug inward and turn the barrel bushing to the right until the plug and the end of the recoil spring protrude from their seat, releasing the tension of the spring. As the plug is allowed to protrude from its seat, the finger or thumb should be kept over it, so that it will not jump away and be lost or strike the operator. Draw the slide rearward until the smaller rear recess in its lower left edge stands above the projection on the thumbpiece of the slide stop; press gently against the end of the pin of the slide stop which protrudes from the right side of the receiver above the trigger guard and remove the slide stop. This releases the link, allowing the barrel, with the link and the slide, to be drawn forward together from the receiver, carrying with them the barrel bushing, recoil spring, plug, and recoil-spring guide.
3. Remove these parts from the slide by withdrawing the recoil-spring guide from the rear of the recoil spring, then draw the plug and the recoil spring forward from the slide. Turn plug to right to remove from recoil spring. Turn the barrel bushing to the left until it may be drawn forward from the slide. This releases the barrel, which, with the link, may be drawn forward from the slide, and by pushing out the link pin the link is released from the barrel.
4.Press the rear end of the firing pin forward until it clears the firing pin stop, which is then drawn downward from its seat in the slide; the firing pin, firing pin spring, and tractor are then removed from the rear of the slide.
5.The safety lock is readily withdrawn from the receiver by cocking the hammer and pushing from the right on the pin part
or pulling outward on the thumbpiece of the safety lock when it is midway between its upper and lower positions. The cocked hammer is then lowered and removed after removing the hammer pin from the left side,of the receiver. The housing pin is then pushed out from the right side of the receiver, which allows the mainspring housing to be withdrawn downward and the grip safety rearward from the handle. The sear spring may then be removed. By pushing out the sear pin from the right to the left side of the receiver the sear and the disconnector are released.
6. To remove the mainspring, mainspring cap, and housing-pin retainer from the mainspring housing, compress the main spring and push out the small mainspring cap pin.
7. To remove the magazine catch from the receiver, its checkered left end must be pressed inward, when the right end of the magazine catch will project so far from the right side of the receiver that it may be rotated one-half turn. This movement will release the magazine-catch lock from its seat in the receiver, when the magazine catch, the magazine-catch lock, and the magazine-catch spring may be removed.
8.With the improved design of magazine-catch lock, the operation of dismounting the magazine catch is simplified, in that when the magazine catch has been pressed inward the magazine-catch lock is turned by means of a screw driver or the short leaf of the sear spring a quarter turn to the left, when the magazine catch with its contents can be removed. The improved design will be recognized from the fact that the head of the magazine-catch lock is slotted.
9. The trigger can then be removed rearwardly from the receiver.
10. The hammer strut or the long arm of a screw driver can be used to push out all the pins except the mainspring-cap pin, lanyard loop pin, and ejector pin.
11. To assemble the pistol, proceed in the reverse order.
12. It should be noted that the disconnector and sear are assembled as follows: Place the cylindrical part of the disconnector in its hole in the receiver, with the flat face of the lower part of the disconnector resting against the yoke of the trigger. Then place the sear, lugs downward, so that it straddles the
disconnector. The sear pin is then inserted in place, so that it passes through both the disconnector and the sear.
13. The sear, disconnector, and hammer being in place and the hammer down, to replace the sear spring locate its lower end in the cut in the receiver, with the end of the long leaf resting on the sear; then insert the mainspring housing until its lower end projects below the frame about one-eighth of an inch, replace the grip safety, cock the hammer, and replace the safety lock; then lower the cocked hammer, push the mainspring housing home, and insert the housing pin.
14. In assembling the safety lock to the receiver, use the tip of the magazine follower or a screw driver to press the safety-lock plunger home, thus allowing the seating of the safety lock. It should be remembered that when assembling the safety lock the hammer must be. cocked.
15. When replacing the slide and barrel in the receiver, care must be taken that the link is tilted forward as far as possible and that the link pin is in place.
(A) Method of Operation
1. A loaded magazine is placed in the handle and the slide drawn fully back and released, thus bringing the first cartridge into the chamber (if the slide is open, push down the slide stop to let the slide go forward.) The hammer is thus cocked and the pistol is ready for firing.
2. If it is desired to make the pistol ready for instant use, and for firing with the least possible delay the maximum number of shots, draw back the slide, insert a cartridge by hand into the chamber of the barrel, allow the slide to close, then lock the slide and the cocked hammer by pressing the safety lock upward, and insert a loaded magazine. The slide and hammer being thus positively locked, the pistol may be carried safely at full cock, and it is only necessary to press down the safety lock (which is located within easy reach of the thumb) when raising the pistol to the firing position.
3. The grip safety is provided with an extending horn, which not only serves as a guard to prevent the hand of the shooter
from slipping upward and being struck or injured by the hammer, but also aids in accurate shooting by keeping the hand in the same position for each shot, and, furthermore, permits the lowering of the cocked hammer with one hand by automatically pressing in the grip safety when the hammer is drawn slightly beyond the cocked position. In order to release the hammer, the grip safety must be pressed in before the trigger is pulled.
(B) Safety Devices
1. It is impossible for the firing pin to discharge or even-touch the primer, except on receiving the full blow of the hammer.
2. The pistol is provided with two automatic safety devices.
3. The automatic disconnector, which positively prevents the release of the hammer unless the slide and barrel are in the forward position and safely interlocked; this device also controls the fining and prevents more than one shot from following each pull of the trigger.
4. The automatic grip safety at all times locks the trigger unless the handle is firmly grasped and the grip safety pressed in.
5. The pistol is in addition provided with a safety lock by which the closed slide and the cocked hammer can be at will positively locked in position.
(C) Operation in Detail
1. The magazine may be charged with any number of cartridges from one to seven.
2. The charged magazine is inserted in the handle and the slide drawn once to the rear. This movement cocks the hammer, compresses the recoil spring, and, when the slide reaches the rear position, the magazine follower raises the upper cartridge into the path of the slide. The slide is then released and, being forced forward by the recoil spring, carries the first cartridge into the chamber of the barrel. As the slide approaches its forward position it encounters the rear extension of the barrel and forces the barrel forward; the rear end of the barrel swings upward on the link, turning on the muzzle end as on a fulcrum. When the slide and barrel reach their forward position they are
positively locked together by the locking ribs on the barrel, and their joint forward movement is arrested by the barrel lug encountering the pin on the slide stop.
3. The pistol is then ready for firing.
4. When the hammer is cocked, the hammer strut moves downward, compressing the mainspring, and the sear, under action of the long leaf of the sear spring, engages its nose in the notch on the hammer.
5. In order that the pistol may be fired, the following conditions must exist: The grip safety must be pressed in, leaving the trigger free to move; the slide must be in its forward position, properly interlocked with the barrel, so that the disconnector is held in the recess on the under side of the slide under the action of the sear spring, transmitting in this position any motion of the trigger to the sear; the safety lock must be down, in the unlocked position, so that the sear will be unlocked and free to release the hammer, and the slide will be free to move back.
6. On pulling the trigger the sear is moved and the released hammer strikes the firing pin, which transmits the blow to the primer of the cartridge. The pressure of the gases generated in the barrel, by the explosion of the powder in the cartridge, is exerted in a forward direction against the bullet, driving it through the bore, and in rearward direction against the face of the slide, driving the latter and the barrel to the rear together. The downward swinging movement of the barrel unlocks it from the slide, and the barrel is then stopped in its lowest position. The slide continues to move to the rear, opening the breech, cocking the hammer, extracting and ejecting the empty shell, and compressing the recoil spring, until it--the slide-- reaches its rearmost position, when another cartridge is raised in front of it and forced into the chamber of the barrel by the return movement of the slide under pressure of the recoil spring.
7. The weight and consequently the inertia of the slide, augmented by that of the barrel, is so many times greater than that of the bullet that the latter has been given its maximum velocity and has been driven from the muzzle of the barrel before the slide and barrel have recoiled to the point where the barrel commences its unlocking movement. This construction, therefore, delays the opening of the breech of the barrel until after the bullet has left the muzzle and therefore practically prevents
the escape of any of the powder gases to the rear after the breech has been opened.
8. This factor of safety is further increased by the tension of the recoil spring and mainspring, both of which oppose the rearward movement of the slide.
9. While the comparatively great weight of the slide of this pistol insures safety against premature opening of the breech, it also insures operation of the pistol, because at the point of the rearward opening movement, where the barrel is unlocked and stopped, the heavy slide has attained a momentum which is sufficient to carry it through its complete opening movement and makes the pistol ready for another shot.
10. When the magazine has been emptied, the pawl-shaped slide stop will be raised by the magazine follower under action of the magazine spring into the front recess on the lower left side of the slide, thereby locking the slide in the open position, and serving as an indicator to remind the shooter that the empty magazine must be replaced by a charged one before the firing can be continued.
11.Pressure upon the magazine catch quickly releases the empty magazine from the handle and permits the insertion of a loaded magazine.
12.To release the slide from the open position, it is only necessary to press upon the thumbpiece of the slide stop, then the slide will go forward to its closed position, carrying a cartridge from the previously inserted magazine into the barrel and making the pistol ready for firing again.
SECTION E. IMPORTANT POINTS
1. Never place the trigger finger within the trigger guard until it is intended to fire and the pistol is pointed toward the target!
2. Do not carry the pistol in the holster with the hammer cocked and safety lock on, except in an emergency. If the pistol is so carried in the holster, cocked and safety lock on, the butt of the pistol should be rotated away from the body when withdrawing the pistol from the holster, in order to avoid displacing the safety lock.
3. The trigger should be pulled with the forefinger. If the trigger is pulled with the second finger, the forefinger extending
along the side of the receiver is apt to press against the projecting pin of the slide stop and cause a jam when the slide recoils.
4. Care must be exercised in inserting the magazine to insure its engaging with the magazine catch.
5. Pressure must be entirely relieved from the trigger after each shot, in order that the trigger may reengage with the sear.
6. To remove cartridges not fired, disengage the magazine slightly and then extract the cartridge in the barrel by drawing back the slide.
7. The pistol must be kept clean, free from rust, and properly oiled. Excessive oil left in the mechanism will cause the parts to gum and work stiffly.
8. Care must be exercised to insure that the disconnector is properly assembled to the sear.
9. The hammer should not be snapped when the pistol is partially disassembled.
10. The grips need never be removed, as the pistol can be dismounted and assembled without removing them.
11. Use no hammer either in assembling or dismounting the pistol.
12. Magazine: Reasonable care should be taken to see that the magazine is not dented or otherwise damaged.
13. Never insert the magazine and strike it smartly with the hand to force it home, as this may spring the base or the inturning lips at the top. It should be inserted by a quick continuous movement.
14. Cleaning solutions and methods are the same as those followed for cleaning the magazine rifle.
Chapter 6. MK. 18 MOD. 1 21-INCH LIGHTWEIGHT DECK-TYPE TORPEDO TUBE AND AUXILIARY EQUIPMENT
1. The torpedo boat is designed to carry four torpedoes in tubes and to discharge them by expansion of ignited gun powder. There are two tubes on each side. Tubes train inboard for cruising and loading, and train outboard for expected action and firing. The forward tubes train outward to an angle of 8° 30' with the ship's centerline, the after tubes to an angle of 12° 30'. All torpedoes are fired forward and at the stated angles with the centerline.
2. Before loading the torpedoes into the tubes, it is intended that the gyro in each torpedo be set to the respective angle of the tube into which it is to be loaded. The direction of setting must be such that after leaving the boat the gyro will correct the course of the torpedo to that of the boat at the instant of firing, plus the spread angle.
3. The boat is designed to release its torpedoes at any speed under any ordinary condition.
4. The following brief description will aid the crew to understand the functions of the various gear:
5. The tube is designed to use the Mark XIV torpedo, diameter, fully charged, 21.060 inches; length, 240 inches; weight in service condition, 3,017 pounds; permissible pressure on afterbody, 100 pounds per square inch.
6. The same torpedo (Mark XIV) with elongated warhead can also be fitted. In this case the length is increased by 6
inches and the weight by 200 pounds. The head is the only part affected by these increases.
7. An alternative torpedo is the Mark VIII-3D, diameter fully charged, 21.060 inches; length with warhead, 250.88 inches; weight in service condition, 3,050 pounds; permissible pressure on afterbody, 75 pounds per square inch (instantaneous only).
8. Before use, the guide stud should be removed, the tapped holes being left open.
9. It is intended that 3" cartridge cases Mark VI be supplied for use with these tubes. The Mark VI case is identical in external outline with the 3" case Mark II, which was designed for 3"/23 caliber guns, except that it had been cut down in length to 6.60 inches. The Mark VI case carries the Mark XX combination primer, which screws into the case. If needed, satisfactory cases may be improvised from Mark II cases, by cutting off to 6.60 inches. The Mark II case, however, carries a primer Mark X or mod., which is arranged for percussion firing only. No attempt should be made to use any other cases than those referred to in the foregoing.
10. The tube proper is made of steel, fabricated by welding. It is pivoted on an aluminum alloy turntable and turntable base. The forward end is mounted on an aluminum alloy support which travels on corrosion-resistant steel plates and is guided by brass Z-bars, cadmium plated. The turntable and the forward support are joined with steel tubing rails. The tube does not recoil.
11. The breech ring and door are of aluminum alloy and are sealed with neoprene gasket inserted in the door.
12. The combustion chamber is a steel casting, tested to 3,000 pounds per square inch for strength and tightness. It is fitted with an interrupted thread piece onto which the firing mechanism locks. With firing mechanism removed, the cartridge should slide into the chamber, when fitted with sealing rings under a moderate hand pressure. The firing mechanism locks it in place. Blow-by around the cartridge is prevented by the
two sealing rings. It is essential that these rings be in place, and free from cuts or gouges, to insure gas tightness. A gasket is provided to keep moisture out of the chamber; this gasket is not designed to prevent blow-by.
13. When the charge is fired, pressure is built up in the chamber and gas is fed into the tube through a throttling orifice located between the chamber and the tube. The tube pressure reaches a maximum soon after torpedo movement begins and decreases gradually to zero as the torpedo clears the muzzle.
14. The firing mechanism is designed for either percussion or electric firing, depending on the type of primer used. The firing pin, which is insulated, is wired to an electric circuit. When the striker bolt is in firing position, it forces the firing pin against the primer, completing the circuit from the control station. The primer may then be fired by hitting the striker knob or by closing the electric circuit with the switch provided at the control station.
15. A projection to engage the starting lever is welded onto & small door over an access hole cut in the tube. This is the tripping latch. The door is held against its seat by four dogs. Guide strips extending aft from the tripping latch to the breech center the torpedo so that the latch and starting lever line up properly. As these guide strips engage the boss on the upper rudder, they also guide the rudder until it is clear of the latch.
16. Torpedo stops are provided to keep the torpedo in place until firing, at which time they shear. This assembly provides for two shear pins to fit into the torpedo guide stud holes. With the rudder located in the before-mentioned guide strips, and the tail hard against the breech door, the stop pins should fit into the two forward holes of the four holes which formerly held the torpedo guide stud.
17. There are, beside the above openings, two charging and access holes cut in the tube and covered by small plates. One
is for Mark VIII and one for Mark XIV. There are in addition openings for setting speed and depth on a Mark XIV torpedo. These openings are modifications according to Bureau of Ordnance specifications.
18. Each tube is equipped with its own training gear. This equipment permits the tubes to be trained inboard so that no part of the tube structure extends over the rail. When action is expected, the tubes are trained outboard, by hand.
19. The training gear consists primarily of a handle-operated corrosion-resistant steel screw which rotates within a swivelling cut made fast to the tube forward support. A stop is provided on each screw which serves to fix the training angle.
20. It is essential that the forward tube be fully trained outboard before the after tube is fired.
21. At the muzzle end, the tube carries two lugs drilled with locating holes. A fixed bracket, also drilled, is mounted on the deck. A removable pin is provided for attaching the tube to the bracket, either in the outboard (trained) position or in the inboard (stowed) position. The purpose of the stop is to relieve the training screw of any load caused by lurching of the torpedo tube in rough water. The pin should invariably be in place when the boat is under way.
22. When preparing to shift the tube by means of the training screw, make certain that the pin has been removed. Bring the holes into exact alignment by means of the screw before attempting to enter the pin. The pin should never be forced into place, and will enter easily when the parts are correctly lined up.
23. For loading, the tube must be trained to an extreme inboard position, and in this condition the locating pin will not be in use.
24. One complete set of gear is provided on each boat to facilitate loading torpedoes into the tubes. This gear consists of three dollies, a height gage and a torpedo strap. The tubes are loaded one at a time, the same loading gear being used for all of them.
25. The dollies are fitted with rollers and jack screws so that the torpedo may be set on them, adjusted to line up with the tube bore, and rolled into the tube. The height gage gives the height to which each dolly should be adjusted. It is applied by dropping into the gaging hole near the center of the dolly. The strap is provided to lower the torpedo onto the dollies.
26. In the loading procedure, each of the three dollies is to-be set on the deck, forward of the tube, in the positions laid out for them and adjusted to the proper height. The loading position of each tube is clearly defined by scribed marks on the forward tube support and the Z guide bars.
Preparation of impulse charge.
27. The regulation charge is 24 ounces of sodium nitrate powder similar to Austin 2-C. Loaded cartridges will commonly be supplied from a depot, ready for use. The following procedure of loading is outlined in case it should be necessary to load cartridges in an emergency.
28. Cartridge cases which have been used in firing should first be washed in a strong solution of cleaning agent similar to Oakite, and dried completely before inserting primers. The loading is to be carried on in a dry atmosphere, not over 50 percent humidity. Powder should be exposed to the air for as brief a period as possible. After loading the case with the specified weight of powder, cover with a cork (or pyralin) wad 1/4-inch thick which has been freshly dipped in melted paraffin. Press down by hand with a tamping tool. Cover with a layer of melted paraffin 1/8-inch thick. Store unused powder and also loaded cartridges in an airtight container.
29. It is imperative that every effort be made to keep the powder absolutely dry. Refrain from handling the powder by hand as it will pick up considerable moisture from the hands.
30. The regulation powder charge (24 ounces) produces an ejection velocity in excess of 40 feet per second, causing the torpedo to clear the deck with a margin of 5 to 6 inches and to dive at the correct angle to insure a successful shot. Should any shot appear to be unduly slow or not to clear the deck by the margin indicated, every item of the charging and loading procedure should be reviewed and checked in comparison with the instructions contained in this pamphlet. Where the Mark
VIII 3D torpedo is used, the regulation charge should under no circumstances be exceeded. To do so would expose the torpedo to probable failure by collapse of the afterbody.
Loading and operation.
31. Train tube to loading position, as indicated by scribed lines on Z-bar and tube forward support. To load the after tubes it is necessary to have the forward tubes in loaded position also; this allows room for the torpedo between the forward tubes and the deck house.
32. Flush the bore of the tube thoroughly throughout its length with light lubricating oil, Navy Dept. Spec. 2110 (SAE #10). Also flush torpedo liberally before loading. Both the tube and the torpedo should be clean before flushing. After removing the torpedo stop assembly, and raising the tripping latch, the tube is ready for loading.
33. Place the loading dollies on the deck forward of the tube at the positions indicated. Adjust the dollies to the proper heights as given by the height gauge, and to the midpoint of their transverse adjustment.
34. Swing breech door aside.
35. Using the strap provided, lower the torpedo onto the dollies. Fasten a nose line to the nose of the torpedo and take a turn around a cleat.
36. Push torpedo into tube until it is near the loaded position. Make certain that the upper rudder enters the guide strips installed in the top of the bore. If necessary, the torpedo may be raised or lowered, and shifted inboard or outboard, with the jack screws in the dolly assembly. Good alignment will enable the torpedo to be pushed into the tube easily.
37. When the torpedo is within a few inches of loaded position, before closing the door, release the propeller lock. Tightly clamp the breech door shut. Then push the torpedo the remainder of the way into the tube until it bumps the door.
38. It is essential that the breech door be firmly closed before the torpedo is brought into contact with it. Should the torpedo accidentally slide to or beyond the loaded position when being pushed in, pull it forward to permit the door to close easily. An attempt to back the torpedo forward by means of the breech nuts will invariably result in gas leakage and a poor shot.
39. Likewise, once the door is closed, it is equally necessary to push the torpedo in the full distance against the door. If this is not done, the tripping latch will not engage the starting lever. The location of the stop pins in the torpedo does not give a reliable indication of the loaded position.
40. When the torpedo is in loaded position (tail piece against breech door) the torpedo stop pins will fit into the two forward holes of the four holes which formerly held the guide stud.
41. Train to stowed position, insert training stop pin.
In loading impulse charge.
42. Place the cartridge in the chamber. It is preferable to grease the cartridge in order to allow it to enter correctly. If the fit is excessively tight or is loose, the reason should be investigated. Before attaching firing mechanism, make sure that the striker knob is in the retracted position. Enter the firing mechanism in the position indicated by arrow. Start engagement of threads and with a strong quick torque on the handles, lock the breech. The breech nut should jam against the cartridge rim while also making light contact with the weather gasket. When ready to fire, turn striker knob 90° and release, allowing striker bolt to bear upon firing pin. This will bring the firing pin into position either for percussion or electric firing, depending on the primer used. If the breech nut is not hard against the cartridge, the firing pin may not reach the primer. In this event, the charge could not be fired electrically and might not fire by percussion.
43. Caution.--Forward tubes must be fully trained outboard when aft tubes are to be fired, to avoid contact of torpedo with forward tube structure.
44. Tube muzzles should have grease packed around the head of torpedo to keep water out.
45. The bore of the tube should be cleaned with varsol or paint thinner and slushed with slushing mixture, as soon as possible after firing. This should be done as a precaution against corrosion, as well as in preparation for reloading.
46. Clean all loose powder residue from combustion chamber walls. Ascertain that the chamber orifice is clean and completely free of any obstructions in the throat.
Check list for loading and operation.
47. The above procedure, for loading and operating are summarized here to be used as a check list.
- Train tube to loading position.
- Ascertain that tube is clean.
- Slush tube and torpedo liberally.
- Remove torpedo assembly.
- Raise tripping latch.
- Place loading dollies in positions indicated.
- Adjust dollies to proper height.
- Lower torpedo onto dollies.
- Secure nose line to nose and take a turn with it around a cleat,
- Remove the wedge which should be behind the starting lever of the torpedo, and set the distance gear off zero. Open stop wide and turn back one-eighth turn.
- Push torpedo into tube within a few inches of loaded position; making certain rudder enters guide strips. (12) Remove the propeller lock.
- Tightly clamp breech door.
- Bump torpedo against door.
- Release stop assembly.
- Secure stop pins and tube.
- Close tripping latch.
- Place impulse charge in chamber.
- With striker knob in retracted position, lock firingchamber mechanism.
- Lower striker knob in firing mechanism, and tube isready to fire.
- Thoroughly clean and slush tube as soon as possibleafter firing. Clean firing chamber and orifice.
Care and preservation of tube structure.
48. The light materials used require special care to preserve them from corrosion and thus to maintain necessary strength. Although all the pinned joints are made in galvanized steel or iron, and in anodized aluminum, they must be kept well greased to forestall chemical attack.
49. Exposed steel surfaces which cannot be painted should be coated with a suitable grease. This applies particularly to the breech door swing bolts, and tripping latch stem, the chamber, and all the pins throughout the complete assembly.
50. Grease should be applied to pressure fittings throughout the assembly at intervals of 1 week.
51. as should be patched. Outside iron and steel parts are to be painted with quick-drying marine primer before applying the outer coat of gray. Aluminum surfaces should be coated with zinc chromate primer and painted with aluminum paint, before applying the gray paint.
52. Zinc blocks attached to forward Z-bar guide strips should have good metallic contact with the surface of the strip, and should remain unpainted. The blocks are to be renewed at intervals after substantial deterioration has occurred.
53. If, for any reason, the weather gasket is removed and replaced, ascertain that the contact between the gasket and the firing mechanism does not prevent tight contact between the block and the cartridge. This is important as the gasket is only to keep moisture out of the breech and is not designed to prevent blow-by.
Chapter 7. MARK 19 TORPEDO TUBE
SECTION A. MARK VIII, MOD. 3 C AND 3 D, MARK XIV AND MARK XV TORPEDOES
1. The Mk. 19 tube is a stationary tube firmly mounted on the deck with the required angle of tube train. This eliminates the necessity of training out the tube before launching of torpedoes.
2. This tube has several points peculiar to it. It has a slot for the guide stud. This is not a T-slot. It is a flat slot and the torpedo must be fitted with a submarine-type guide stud--that is, a flat guide stud. The slot goes only to the stop pad.
3. The tube has no breech door. It has a screw plug about 6 inches in diameter for access to the tail. This should be open when loading and putting on positive lock. After lock is on, it can be set up.
Note: Tubes of later manufacture will have breech doors.
4. This tube also has rollers. The rollers are mounted on eccentric pins. The pins are locked in the desired position by washers carrying small lugs which ride in holes in the castings. The torpedo must be in the tube before these can be adjusted. The eccentric pins are turned until the desired "height" is obtained. The pins should carry a scribe mark to show whether they are in the "up" or "down" position. If the rollers are in the fully down position the stop mechanism will not engage. They must be slightly raised. There are four rollers. Usually they will be at different heights, since the center line of the rollers is not uniform and the tube may sag.
5. Compressed air replaces the powder impulse charge used in launching from other tubes. A pressure of 230 pounds per square inch is used in launching Mark VIII-3C and 3D and Mark XIV torpedoes, and of 240 pounds per square inch for launching Mark 15s and 15--1s. The flask may be charged from the air flask of the torpedo, from the boat's compressor, or from a transportable pressure flask, through charging valve on flask.
After charging, the pressure will drop due to cooling. An allowance of from 5 to 6 pounds should lie made for this; and, if the tube is not to be fired within 12 to 16 hours, an additional 5 to 10 pounds should be carried. The average leakage over a period of 24 hours is approximately 10 pounds.
6. The stop mechanism for this tube is contained in the stop mechanism housing mounted at top center on the tube at the position of the guide stud on the torpedo air flask. Two pads for securing this mechanism are provided, one for Mark VIII and Mark XIV torpedoes and the forward pad for Mark XV.
Torpedo Tube Train Angles
Boat type Train angle Gyro angle for
unit of spread
Elco 80' Port forward tube 81/2 L 8 R. Starboard forward tube 81/2 R 8 L. Port aft tube 121/2 L 11 R. Starboard aft tube 121/2 R 11 L. Higgins Port forward 12 L 111/2 R. Starboard forward 12 R 111/2L. Port aft 12 L 101/2 R. Starboard aft 12 R 101/2 L. Huckins Port forward 10 L 91/2R. Starboard forward 10 R 91/2 L. Port aft 121/2 L 11 R. Starboard aft 121/2 R 11 L.
The stop lever is held in place ahead of the stop on the torpedo by a replaceable breaking link, when the tube is ready for firing. A positive lock is provided aft to prevent possible shearing of the link before you are ready to fire. This lock must be released when the tube is fully ready for firing.
7. The air is released into the after section of the tube upon firing by either local or bridge control, by means of a direct
hydraulic tube and two pistons which open the release valve in firing.
When the main valve and route valve are' open, air is banked up above the main valve piston seating the piston and isolating the air in the flask. When the release valve is thrown, this pressure is vented, permitting flash pressure to unseat the main piston and to pass into the tube, forcing the torpedo forward.
8. The access holes in the tube consist of the following: breech plug, oil-filling plug, tripping latch, depth setting, speed setting, two stop- and charging-valve holes, and the stop-mechanism flange.
9. In using Mark VIII-3C and 3D arid Mark XIV torpedoes the stop mechanism should be put on the after pad. The stop and charging valves for Mark VIII and Mark XIV torpedoes will be under the after stop and charging access hole.
The oil pot filling hole for Mark VIII-3C and 3D will be under the pad in the center of the tube farthest aft. The tripping latch and depth-setting holes are the same for Mark VIII, Mark XIV, and Mark XV torpedoes.
SECTION B. PREPARING MK. 19 TUBE FOR FIRING
1. Take off positive lock, until the threads are disengaged from the split sleeve in the back of the stop mechanism housing.
2. Open route valve by turning counterclockwise until handle is down against packing gland nut.
3. Operate extractor control once or twice, thereby popping the release valve to assure proper operation of hydraulic control.
4. Back off the main valve stem as far as possible.
5. Tube is ready to fire by throwing extractor control over.
If packing gland and route valve are tight, this tube could be held ready for firing indefinitely, but care must be exercised in not moving the hydraulic control, which has only a short distance to go in firing the torpedo.
SECTION C. SAFETY PRECAUTIONS
1. Never start preparing the tube for firing without completely backing off the positive lock on the stop mechanism.
2. Never try to load the torpedo without lifting the stop lever clear of the tube and lifting the tripping latch off the tube.
3.After each firing, the firing valve should be checked before recharging, since firing will often jerk the neoprene piston washer out of its recess. Also the cylinder must be absolutely clean to insure proper operation of valve.
4. The exactor control hydraulic system should be checked frequently for presence of air. This is evident when the transmitter handle will not stay in the after position. This indicates leakage and calls for checking valve assembly.
5. In installing and adjusting tension link, take care that no pressure is exerted in tightening tension link adjusting nut as it will strain the cutaway section of the tension link, and cause it to part prematurely.
6. Check packing glands on main valve and route valve daily for leakage.
SECTION D. LOADING
This tube was designed to be removed from the boat for loading as on a dock or tender. The tube is then replaced on the boat. In calm water with a good crane operator the tube can be loaded without removal. With inexperienced personnel this is not advisable initially. With some experience the danger decreases.
The following steps should be taken in loading the torpedo tube on a dock or tender:
- Disconnect hydraulic line at the bottom of the exactor control receiver on the side of the firing valve.
- Remove the eight mounting bolts at the forward and after bracket pads.
- Put on the three-legged sling, the long leg going aft to the after lifting pad just aft the stop and charging valve access hole; the two short legs going forward to the lifting pads on each side of the forward bracket pads.
- Hook on with the crane and remove the tube from the boat and set in either wooden chocks or on a set of mounts on the dock.
- Lift the stop mechanism lever clear of the tube and into the stop mechanism housing. This is done by pushing down lever handle (part No. 78) until part No. 80 can be put under the forward end of lever handle to assure its staying up until after the torpedo is in position in the tube.
- Remove the tripping latch from tube.
- Remove the breech plug.
- Attach loading winch to the breech of the tube.
- Unreel wire rope on the loading winch and pass through tube to be hooked onto the tail of the torpedo.
- Raise the torpedo to the proper height and pull into the tube with the loading winch until the torpedo is in position. The torpedo is allowed to go approximately 1 inch past its neutral position thereby making it easier to remove the wire rope from the tail of the torpedo.
- Insert breech plug and bring torpedo to its neutral position.
- Remove the wedge from the tripping lever and put on tripping latch.
- Remove catch from stop lever handle and bring stop lever down in front of the guide stud.
- Remove tension link adjusting nut and insert tension link into the adjusting nut.
- Replace the adjusting nut and insert opposite end of tension link in the stop lever yoke.
- Insert positive lock (part No. 84) by screwing clockwise until stop lever is hard against the front of the guide stud and clamp with locking screw (part No. 88).
- Bring up tension link adjusting nut fingertight and lock by screwing down locking screw (part No. 92) firm against tension link adjusting nut.
- Pick up torpedo tube and return to mounts on boat, letting the forward bracket pads come into place first and then letting the tube down where the after bracket pads come into place.
- Insert forward mount bolts and pull elastics top nuts down tight.
- Put on chaffing plate with rubber cushion between the two chaffing plates. Insert mount bolts through the mount bracket pad in the chaffing plates. Put on jam nuts, bring them down handtight then put on the elastic stop nuts, jamming the elastic stop nuts with the jam nuts, thereby leaving the mount free to work fore and aft as the deck of the boat works under the tube.
Chapter 8. .50 CAL. BELL AIRCRAFT MOUNT
1. The Bell Aircraft twin cradle for .50-caliber machine guns is a flexible, lightweight, scarf-ring type mount equipped with a hydraulic system to absorb recoil shock. It is designed to be fired by either or both hands. It is manufactured in accordance with Bell Aircraft Corporation drawing 03-038-075.
2. The cradle frame is made up of four parallel bearers on which are assembled front and rear trunnion slides. Four shock unit assemblies (two for each gun) are attached, at their forward ends to the rear trunnion slides. At the rear they are attached to the cradle back plate support.
3. Deflector assemblies are bolted to the bearers and support a yoke and chute assembly serving both guns. Bolts holding outer ends of deflector brackets to bearers also hold continuous feed rear brackets in place.
4. The cradle back plate houses trigger and safety mechanism, including trigger-synchronizing adjusting screws. This back plate is easily removed by loosening knurled nut on bottom of cradle back plate support, and the two knurled screws at the top of the hand grips.
5. The mount for the twin cradles is housed in a barbette or stand whose circumference is 44 inches. The stand itself contains a roller ring or base built around the inner diameter--the brake band--and carries thereon a roller path. The base of the mount fits inside and next to the brake band at the top portion of the stand. In so fitting, the roller path is encased by the mount base or ring. To provide easy and smooth operation and to anchor the mount there are 24 bearings mounted in the base ring of the mount and moving in the roller path. These consist of one horizontal and one vertical roller mounted on a small plate. The horizontal one rolls against the side of the V-shaped roller path and prevents other than circular motion in the horizontal plane. The vertical roller rides against the bottom surface normally and supports the mount. However, if the mount moves upward from
shock, the roller rides against the top surface and thus anchors the mount. The small plate on which the rollers are mounted is secured to the bottom ring of the mount by two screws. It should be pointed out that if it becomes necessary to lift the mount it is necessary to first remove these bearings.
6. The mount has a train of 360° but may be secured in any position by a hand-operated brake. This brake is located just above the base of the mount, being attached thereto, and next to the brake band. It is just to the left of the gunner. Its operation consists merely of moving a hand lever to the ON position. This movement operates two eccentric cams. The motion of the cams pushes out a brake bar which in turn, by means of springs, pushes outward on the brake shoe. The brake shoe rests against the inside of the brake band preventing further movement of the mount. It may be applied in any position of the 360° train. In addition the mount may be locked in one definite position by inserting four securing bolts into four equally spaced threaded holes in the top of the scarf ring. These bolts fit into threads in the roller path which are in line with the holes of the scarf ring.
7. The twin guns may be elevated to an angle of 85° and depressed to an angle of 5°, the angle of depression ceasing when the guns come to a rest against the top of the stand. However, certain sections of the stand are higher than others. These elevated sections are so placed in order to prevent the guns being fired on any part of the boat. When not in use, the guns are locked in a vertical position by means of a securing spring bolt attached to the mount and setting into a bar between the two guns.
The training of the mount is operated by the movements of the gunner. Directly in back of the guns, and attached to the inside of the mount, is a back rest. The gunner, having his back placed therein, automatically turns the mount to the right or left by his own corresponding movements.
Functioning of Hydraulic Shock Units
1. The purpose of the hydraulic shock unit is to reduce recoil shock produced by gun fire. This is accomplished by combining
the functioning of an hydraulic piston with the reaction of a specially designed recoil spring.
2. When firing, with gun in level position, the major portion of the recoil shock is absorbed by the action of the hydraulic piston--the spring serving to return the gun to normal position after recoil.
3. Firing at a declined angle, recoil is counteracted by the hydraulic piston and weight of the gun.
With the gun in an inclined position, the spring offsets the weight of the gun and recoil shock is absorbed by the hydraulic piston.
Maintenance of Mount
1. Upon delivery of mount, it should be immediately painted and all bare surfaces should first receive a coat of red lead.
2. Once every quarter, the brake should be taken down and thoroughly cleaned.
3. Springs in the trigger mechanism should be taken down and cleaned whenever necessary.
4. Link deflector should be checked for proper size.
5. Bearings should always be thoroughly greased. A supply of bearings should be kept on board to replace any breakage that may occur.
Chapter 9. DEPTH CHARGES
Description and Operations
1. Depth Charges Mark VI (Plate 1).--The depth charge Mark VI contains a 300-pound cast TNT main charge with a 3.5-pound booster charge and is of the same size as the depth charges Mark II, Mod. 2, and Mark III. Each depth charge consists of a galvanized steel case, Mark VI, having a central tube within which are assembled the pistol Mark VI with percussion detonator Mark I, Mod. 1, the booster extender Mark VI, and the booster can Mark VI. The depth charge Mark VI may be distinguished from the depth charges Mark II, Mod. 2, and Mark III by the annular groove located near each end of the case Mark VI. The depth charge Mark VI will fit the depth charge release tracks Marks I and III and may be used with the depth charge projector Mark I (Y-gun), the same as depth charge Mark II, Mod. 2, or Mark III but the pistols and booster extenders Mark VI are not interchangeable with similar components Mark II, Mod. 2, or Mark III.
2. Case Mark VI.--The depth charge case Mark VI is fabricated from sheet steel rolled to shape and welded along a longitudinal seam, forming a cylinder 17.625 inches outside diameter by 27.625 inches long. Near each end of the case a bead is rolled, forming seats for the pressed sheet steel heads, which are spot welded and also edge welded to the case. A steel flange fitted with a pipe plug is welded to each head for filling purposes. A forged steel flange is welded to each end of the seamless central tube and to the center of each head, forming the seats for the pistol and booster extender. The central tube is made heavier than in previous depth charges to eliminate distortions due to filling and handling. No holes, other than the filling holes, enter the explosive space, eliminating sources of exudate leakage. The U-bolts, provided in the heads of
Figure 21.--Depth Charge Mk 6.
previous depth charges for handling purposes, have been eliminated from the Mark VI cases, as experience has indicated that the charges can be handled by slings or barrel clips. The entire case is hot galvanized inside and out, after fabrication. Blank covers are provided to seal the central tube during shipment or whenever the pistol or booster extender are removed.
3. Pistol Mark VI.--(a) The depth charge pistol Mark VI embodies, in principle, the general design features of the pistols Mark II, Mod. 2, and Mark III. All parts except the springs are made of nonferrous materials and are generally more rugged to withstand handling and testing. The pistol Mark VI is not interchangeable with pistols Mark II, Mod. 2, or Mark III.
(b) Operations.--With the index pointer set for the depth desired, and with the knob of the safety cover knocked off, water will enter through the inlet valve parts, filling the space within the bellows and bellows extension. As the charge sinks, the hydrostatic pressure increases, overcoming the resistance offered by the firing spring and causing the hydro piston and stem to move inward, toward the detonator end. As the piston and stem continue this movement, the spring-engaging collar located at the outboard end of the piston stem will contact the depth setting spring, the instant of contacting depending upon the index pointer setting. For the 30-foot setting, the depth setting spring is not contacted, all resistance to pressure being offered by the firing spring, release plunger spring, and inherent resistance of the bellows. The piston stem eventually contacts the end of the release plunger, compressing the release plunger spring, allowing the lock balls to recede into the space formed by the reduced diameter of the release plunger. As the lock balls recede, they disengage the countersunk end of the guide tube bushing, allowing the entire firing plunger assembly to move forward under the impulse of the compressed firing spring, until the firing point strikes the detonator. When the index pointer is set to SAFE, the spring adjusting bushing is raised to such a position that, when pressure is applied within the bellows and the piston moves forward, the spring engaging collar will contact the rim of the spring adjusting bushing before the plunger lock balls are released, thus preventing the pistol from firing.
(c) Due to the necessity for compressing the depth-setting spring slightly when setting the index pointer to SAFE, more force must be exerted upon the index pointer than can readily be exerted by hand or fingers. A depth setting wrench is provided to permit convenient setting of the index pointer to all indexed positions.
(d) The pistol has eight indexed settings stamped upon the face of the carrying flange, namely, 30, 50, 100, 150, 200, 250, and 300 feet, respectively, and SAFE. The index pointer has two accurate slots through which pass the machine screws which engage tapped holes in the index carrier. This arrangement allows calibration of the depth setting mechanism to be made during tests without disturbing the index pointer dial setting.
(e) The pistol-carrying flange is a bronze forging drilled for eight machine bolts and threaded for the attachment of cooperating parts. A thin, hard gasket is used between the case and the pistol flanges, to eliminate troubles formerly experienced due to canting of the mechanisms in the central tube of the case when the securing bolts were set up unevenly.
(f) The pistol bellows is larger than those used in previous pistols, in order that a 30-foot setting might be obtained when the same strength of firing spring is used. Due to the increase in size of bellows, the depth-setting spring and associated sleeves are heavier than those of the pistol Mark III. The depth-setting sleeve engages the adjusting bushing through a single-thread screw having a pitch of 0.90 inch.
(g) The firing plunger locking balls rest against the countersink of the replaceable guide tube bushing, allowing restoration of the guiding surface in case of excessive wear. The method of securing the detonator is different from that of the earlier depth charges, necessitating the use of a pin wrench for assembling. The centering flange at the end of the guide tube provides a flat surface against which the booster can move about when in armed position.
(h) A new feature is the inlet valve, intended to protect the pistol against countermining. Normally, this valve is kept off its flat seat by a spring, but under the influence of a suddenly applied abnormal pressure, the valve is intended to seat, preventing
entrance of water into the bellows space during the interval that the abnormal pressure acts.
(i) A light brass screwed cover is provided to protect the water entrance parts during storage, while a similar cover, having an extension knob, is provided for use only when the charges are located in the release tracks. This knob is intended to be wiped off by the wiping plates on the release tracks, exposing a hole in the cover and permitting the entrance of water into the bellows space.
(j) Instructions relative to routine inspection, tests, overhaul, and repair of pistols Mark VI are contained in part II of this pamphlet.
4. Booster extender Mark VI.--(a) The booster extender Mark VI is, in general, similar to the booster extender Mark III insofar as its operation is concerned. All parts except the extender springs are of nonferrous materials. Forged bronze flanges have been substituted for pressed steel and a thin hard gasket is used instead of the former thick rubber gasket. The extender mechanism is not permanently attached to the booster can, as in the older mechanisms, but is provided with a flanged collar for engaging a socket on the booster can when assembled in the depth charge case. The booster extender Mark VI is not interchangeable with booster extender Mark II, Mod. 2, or Mark III.
(b) Operation.--When the safety fork is removed from the booster spindle, the bellows, assembled under compression, will elongate approximately 0.25 inch, causing the booster spindle to move inward, opening up a passage for the entrance of water around the reduced outer portion of the booster spindle. This inward motion is permitted by the necked portion of the booster spindle in wake of the locking balls. As the charge sinks, the increase in hydrostatic pressure overcomes the resistance of the extender spring and bellows until the locking balls enter the enlarged bore of the spindle guide. With the balls thus released from the engagement with the shoulder of the booster spindle, the extender bellows is free to extend its full travel, under the influence of the existing hydrostatic pressure, forcing the end of the booster can against the centering flange of the pistol. At this time the detonator is housed within the detonator envelope.
(c) Two safety forks are furnished with each booster extender Mark VI. One fork is plain, for use during transportation and storage, while the other is knobbed, for use when live charges are installed in the depth charge release tracks. (See par. 33 (b) of ordnance pamphlet No. 721, Depth Charge Release Gear Mark III.) With either safety fork in place on the booster spindle, the extender bellows is compressed and the booster spindle practically fills the bearing hole in the spindle bushing, immediately under the fork. This combination prevents the entrance of foreign matter into the bellows space. A hole is provided near the end of the booster spindle to allow the use of a spindle retracting tool when assembling the safety fork.
(d) The booster extender will function, causing the booster can to move into engagement with the detonator, when the depth charge has reached a depth of between 12 and 15 feet.
(e) Instructions relative to routine inspection, tests, overhaul, and repair of booster extender Mark VI are contained in part II of this pamphlet.
5. Booster can Mark VI.--(a) The booster can Mark VI contains approximately 3.5 pounds of granular TNT, and consists of four parts, the can itself, the detonator envelope, and the head and the socket attached to the head for engaging the flanged collar on the booster extender mechanism Mark VI. The booster can Mark VI is not interchangeable with booster cans Mark II, Mod. 2, or Mark III.
(b) Six inverted dimples pressed in the booster can are used for centering the can in the central tube of the case.
(c) The head is locked mechanically to the booster can, after loading by means of four pressed lugs which engage in corresponding "bayonet slugs" pressed into the can near its open end, to relieve the strains otherwise imposed upon the soldered joint during handling. Air and watertightness of the joint between the can and head is effected by the use of low melting point solder applied with steam heated soldering irons at the loading depots.
(d) The booster can Mark VI is designed to permit the loading and handling apart from the inert booster extender mechanism.
(e) Instructions relative to routine inspection, test, overhaul, and repair of booster cans Mark VI are contained in part II of this pamphlet.
6. Stowage of depth charge components aboard ship.--(a) Pistol stowage box.--Depth charge pistols Mark VI, when not assembled in the depth charge cases, are to be stowed in the pistol stowage box furnished for that purpose. When stowed, the plain inlet valve cover cap should be in place, the firing plunger in the "cocked" position and the index pointer set at "30". The pistol stowage box is fitted with notched battens so arranged as to provide stowage for a maximum of 12 pistols, together with the necessary knobbed safety covers. Less than 12 pistols may be stowed, depending upon the allowance issued for the individual vessels. The pistol stowage box should be kept locked and in a safe, dry place.
(b) Booster stowage can.--Booster extender mechanism and booster cans, when not assembled in the depth charge cases, are stowed together in booster stowage cans. When stowed in the stowage cans, the plain safety fork should be fitted to the booster extender, and the knobbed safety fork placed on the centering ring.
(c) Detonator stowage box.--Percussion detonators Mark I, Mod. 1 (65 grain) will be supplied in wooden stowage boxes. Each wooden box contains a total of 12 detonators, 6 of which are packed in each of two copper boxes. The wooden stowage boxes will be stowed in the lockers provided for that purpose in the vessel.
7. Service tools.--Each vessel equipped for launching depth charges Mark VI will be furnished a set of the following tools packed in a canvas set:
Depth setting wrench.
Detonator holder wrench.
Extender testing tool.
8. Safety features and results of tests.
(a) A depth charge pistol, Mark VI, when set on SAFE, sustained a pressure of over 600 pounds per square inch before the pistol bellows were ruptured. This pressure corresponds to a depth of approximately 1,350 feet in sea water.
(b) A depth charge pistol, Mark VI, when assembled in a depth charge case, and dropped so that the booster end of the case landed upon timber laid over concrete, functioned as follows:
Depth setting Height of fall Result 30 feet 6 feet Fired. 300 feet 15 feet Fired. Safe 24 feet Did not fire.
(c) A booster extender, Mark VI, with the safety fork in place, sustained a pressure of 600 pounds per square inch before the booster spindle pulled through the safety fork. This pressure corresponds to a depth of approximately 1,350 feet of sea water.
(d) A loaded booster can and booster extender, Mark VI, without safety fork, when assembled in a depth charge case, and dropped so that the pistol end of the case landed upon timber laid over concrete, functioned when dropped in a distance of 2 feet, allowing the booster can to assume its "armed" position.
(e) From the foregoing, the necessity for protecting a loaded and primed depth charge against dropping on end is evident. However, if the pistol fires, the booster can will not be in the armed position, and the detonator will explode in the "safety space" provided. On the other hand, if the booster can reaches its armed position, due to a blow or drop, the pistol will not fire. The safety cover and safety fork should invariably be in place whenever live, primed depth charges are handled.
9. Effect of underwater explosions.--On plate 9, O. P. 747, are shown the relations existing between the weight of charge, the distance from charge to hull, and the relative damage expected to be inflicted upon submerged and surface vessels. The data shown are the results of experiments conducted by the Bureau of Ships.
30 feet Fatal damage. 50 feet Serious damage. 90 feet Moderate to slight damage.
10. Sinking rates of depth charges.--The rates at which depth charges sink depends upon the condition under which they are launched, the average sinking rate in disturbed water, as in
a ship's wake, being less than charges launched in still water. The approximate average sinking rates are as follows:
Conditions of launching Sinking rate
(feet per second)
Mark VI (300 lb.)
In still water 9 feet. In disturbed water 6 feet.
11. Weights of depth charge components.--
Pounds Case, Mark VI empty 90.0 Case, Mark VI, loaded, unprimed 390.0 Case shipping covers 2.0 Pistol, Mark VI 17.5 Booster extender, Mark VI 7.5 Booster can, Mark VI, empty 1.7 Booster can, Mark VI, loaded 5.2 Detonator box, with 12 detonators 1.3 Pistol stowage box, empty 50.0 Booster stowage can, empty 2.0 Depth charge, Mark VI, loaded and primed 420.0
Testing, Overhauling, and Repairing
12. General description of testing sets and tools.--(a) With these testing sets air pressure can conveniently be applied to those working parts of pistols and booster extenders which, in service, would be subjected to water pressure. Thus it is possible to discover leaks if they exist and to check the pressure, and therefore the depth, required to operate the booster extender or to fire the pistol. Besides containing the apparatus for testing the pistols and booster extenders, each testing set also contains certain tools that will aid in the assembly, disassembly, and preparation for use of the depth charge material.
(b) In addition to the above-mentioned testing sets, a tool set is provided for use aboard all ships equipped for launching depth charges. This set consists of three tools packed in a canvas bag. These tools are duplicates of tools included in both of the testing sets.
13. Testing set, Mark II.--The depth charge testing set, Mark II, consists of the following parts and tools:
- Testing set holder.
- Cover, which is provided with a small pressure gage and an auto tire valve.
- Clamping piece.
- Depth setting wrench.
- Detonator holder wrench.
- Extender testing tool.
- Cocking tool.
- Extender stop.
- Firing plunger sleeve.
- Rubber washers (2).
- Air pump with 6 feet of tubing.
- Socket wrench.
- Extra valve stem.
- Two boxes of valve insides.
- One box of valve caps.
- Tool box.
14. Service tool set.--The tool set for use on board all ships equipped for launching depth charges consists of the following:
- Depth setting wrench.
- Detonator holder wrench.
- Extender testing tool.
- Canvas bag.
15. Care of the testing sets.--The apparatus and tools comprising the testing sets should be kept in the box provided for them when not in actual use. Attached to the under side of the lid of each box is a list of tools which furnishes a ready reference for checking the contents of the box. Care should be taken when using the tools not to strain them beyond their capacity. The pressure gauge should be compared occasionally with a standard gauge to see that its readings are approximately correct.
Instructions for Testing Pistols and Booster Extenders
16. General instructions.--Stations issuing depth charges should test pistols and booster extenders before issuing them to
the service. Tenders should inspect and test pistols and booster extenders that have been in storage for any considerable period before issuing them for use with loaded depth charge cases.
17. Testing the pistol.--(a) Remove the inlet valve cover and detonator (if present) ; see that the detonator collar and detonator holder are in place and set the index pointer at the 100-foot setting. Do not test pistols at a setting greater than 100 unless instructed to do so by the Bureau of Ordnance.
(b) Cock the pistol if it is not already cocked. Use the cocking tool.
NOTE.--A pistol is cocked when the firing plunger is in the ready position. If the firing plunger is not in the ready position it can be returned to the ready position by pushing the plunger inward against the reaction of the firing spring until it locks itself in position. (Use the cocking tool.) The relation of the shoulder on the cocking tool to the centering flange on the pistol will indicate whether or not the pistol is cocked. If the tool is stopped by the plunger so that the shoulder on the tool is flush with the face of the flange, the pistol is cocked. If the shoulder is about 0.75 inch from the face of the flange, the pistol is not cocked.
(c) Clamp the testing set holder in a vise with the larger opening up.
(d) Assemble the following in the holder in the order named:
- Rubber washer (largest outside diameter).
- Depth charge pistol.
- Rubber washer (smallest outside diameter).
- Clamping piece.
(e) See that all the parts are centered relative to each other and that the cover is resting flat on its washer, then clamp all together by turning the clamping piece to the right until tight.
(f) Attach the pump to the valve in the cover and pump air into the mechanism until a pressure of 30 pounds is obtained.
(g) Observe the pressure gage reading; if it is apparent that the system does not leak, or if the loss is not more than 5 pounds in 1 minute, the pistol mechanism is sufficiently tight.
(h) If the system fails to hold the pressure, the leak may be
in the testing set and care should be taken to see that this is made up tight and that the auto tire valve is not leaking.
(i) If the leak persists the pistol should not be used but should be tagged and laid aside for overhaul. If this test is being made aboard ship, return the pistol to a depot for replacement.
(j) If the pistol proves to be airtight, proceed as follows to determine the depth at which it "fires":
- Pump air slowly into the testing set until the pistol"fires": The "firing" of the pistol is indicated by a pronounced click caused by the firing plunger striking the detonator holder collar.
- Note the reading of the pressure gage when this occurs. A pressure of 44.4 pounds per square inch is equivalent to 100 feet of sea water, and a reading on the test gage of not less than 42 pounds and not greater than 47 pounds when the pistol "fires" will indicate a satisfactory pistol.
The gage should be watched closely for the exact reading when the pistol "fires," as it is difficult to stop pumping at this instant, especially if the pistol "fires" on the beginning of a down stroke of the pump.
(k) Disconnect the pump and allow the air to escape by depressing the plunger in the tire valve before the clamping piece is loosened.
(l) Remove the pistol from the testing set. Cock the firing-plunger and replace the inlet valve cover.
(m) If the firing pressure conforms to the figures given above, the pistol is satisfactory. If it does not conform to these figures and the test is being made aboard a ship, the pistol should be returned to a depot for replacement. If the test is being made at a depot, lay the pistol aside for overhaul.
(n) Depth charge pistols should be tested only as authorized, because continued working of these mechanisms will distort the metal bellows and produce unnecessary wear on the plunger-releasing mechanism. A pistol to be used for instruction and drill is availa.ble to all tenders.
OTE.--The gage on the cover of the testing set should be checked occasionally, especially if the readings taken on a series of pistol tests are consistently high or low.
18. Testing the booster extender.--(a) Remove the safety fork from the booster extender, then hook the extender stop, on the booster spindle. This can be easily done by pressing on the booster connecting collar of the booster extender so that the groove in the booster spindle is extended above the face of the flange.
(b) Secure the holder of the depth charge testing set in a vise and assemble the booster extender with rubber washers, cover, and clamping piece exactly as in testing a. pistol.
(c) Pump air into the system until the booster spindle is released from the locking slide and extends to the full travel permitted by the extender stop. If this occurs at a pressure of 4 to 8 pounds per square inch, the action of the booster extender is satisfactory.
(d) After testing the booster extender for the unlocking pressure, continue to pump air into the system until a pressure of 20 pounds per square inch is obtained. Observe the mechanism for leaks. If the indicated pressure on the gage does not drop more than five pounds in one minute, the mechanism is satisfactorily tight. If the test indicates that the mechanism leaks, it should be laid aside for overhaul if the test is being made at a depot. If aboard ship, return the booster extender to a depot for replacement.
NOTE.--When making leak tests and leak is observed, be sure the leak is not in the testing set.
(e) A booster extender to be used for instruction and drill is available to all tenders.
19. Use of the service tool set aboard ships.--Three tools are furnished for use on board ships equipped for launching depth charges. These tools are packed in a canvas bag and are kept In the pistol stowage box.
(a) Depth setting wrench.--This is a flat wrench designed to engage the pistol index pointer so that it may be easily turned to any desired setting. The wrench will fit on the index pointer in only one way, that is, with the pointer end (marked "A") in the cut-out part of the wrench opposite the handle. This permits visual inspection of the index when it is being turned to a particular setting.
(b) Detonator holder wrench.--This wrench is designed to screw or unscrew the detonator holder when detonators are installed in, or removed from, the pistol.
(c) Extender testing tool.--This tool has a twofold use: (1) to aid in removing and changing the safety forks, and (2) to test the freedom of the booster extender after it is mounted in the depth charge.
(1) Removing and changing safety forks.--Plain safety forks can be pulled from the booster spindle by engaging the hook on the tool in the hole in the safety fork. After the safety fork is removed from a booster extender mounted in a depth charge, the spindle will spring inward about one quarter of an inch. Use the hook on the extender testing tool to pull the spindle outward so that the safety fork to be installed can be engaged with the groove in the spindle.
(2) Testing the booster extender.--Remove the safety fork, engage the hook of the testing tool in the hole at the end of the booster spindle and pull outward. Hold outward on the spindle and swing the body of the tool until the recessed end engages the groove in the spindle. Release the tension on the tool and the booster spindle will retract and pull the body of the tool into the hole in the flange. The hook will now be free; swing it outward to clear the flange. Test the booster for freedom of motion by pushing the spindle inward about an inch. To release the tool from the booster spindle, engage the hook on the tool in the hole at the end of the spindle. Pull outward on the hook and disengage the body of the tool from the spindle by swinging it outward and away from the spindle. The hook can now be released.
Routine Inspection and Overhaul of Depth Charges
20. General instructions.--All depth charge material shall be given a. routine inspection and overhaul by depots prior to issuing the material, and by ship's personnel when preparing the material for use. In general this overhaul will consist of cleaning, oiling, and testing the material and the making of minor repairs. Major repairs should be made only by shore
stations which have been authorized to make these repairs and which have been supplied with special tools for the purpose.
21. Inspection and overhaul of cases.--(a) Remove the pistol, booster extender, and booster from the depth charge case. Removing these mechanisms will be necessary only on board ships during war, as, during peacetime, they will be carried in their designated stowage spaces.
(b) Inspect the case carefully for leaks of TNT exudate. If any leaks occur they will probably be at the welded seams or around the pipe plugs at the ends of the case. If leaks occur in cases aboard ship, or at shore stations, the Bureau of Ordnance should be consulted for instructions as to disposal.
(c) If no leaks are found, check the diameter and length of the case to see that these measurements are within the allowed tolerances. See that the pipe plugs do not project beyond the plane of the ends of the case.
(d) Inspect the central tube and see that it has no projections or deformations which would prevent the free motion of the booster can or proper assembly of the pistol.
(e) Depots shall provide themselves with a cylindrical plug gage to be used in gaging the central tube of the loaded depth charge cases. This gage shall have a diameter of 4.160 inches (plus 0.003, minus 0.000), and a length of 8.75 inches (plus or minus 0.030), and it shall enter and pass freely throughout the length of the central tube.
(f) Inspect the tapped holes in the flanges at the end of the central tube. If the bolts come out freely when the covers are removed it will indicate that the threads are in satisfactory condition.
(g) Inspect and clean the gasket seats on both ends of the case to insure that the assembly can be made watertight.
(h) Inspect the gaskets and see that they are in good condition.
(i) If a depth charge case does not conform to the proper dimensions or is unsatisfactory for any reason and it is being overhauled by a depot, set it aside for repair or, if being overhauled by a ship, return it to a depot for replacement.
22. Inspection and overhaul of pistols.--(a) Test the pistol as directed in the instructions for testing
pistols. If the pistol passes this test satisfactorily it is ready for service use.
(b) If the pistol fails to function satisfactorily, examine the firing plunger and firing spring. To do this remove the detonator holder locking spring, the detonator holder, and the detonator collar. Set the index pointer at 30 and mount the pistol in the depth charge testing set and "fire" the pistol. Hold a piece of wood at the end of the guide tube to catch the blow of the firing plunger. Remove the firing plunger and the firing spring.
(c) See that the locking balls are in position in the firing plunger and that they are in good condition.
(d) Examine the release plunger for ball indentations by pressing inward on the locking balls with the fingers and at the same time rotating the release plunger relative to the firing plunger. If the release plunger has any ball indentations, they can be felt as the plunger is turned. If the balls are allowed to lie in these depressions when the firing plunger is assembled for service, the pressure required to operate the pistol may be changed.
(e) Set the release plunger in a position where the balls do not rest in depressions.
(f) Clean the inside of the guide tube thoroughly and lubricate it with a light coat of oil.
NOTE.--All oiling should be done with a light bodied lubricating oil equivalent to Federal Standard Symbol 2110 (see Bu. Eng. pamphlet, N. Eng. 31). Wet a cloth with oil and rub the cloth over the surfaces to be lubricated. Do not "flush" with oil, but use it sparingly.
(g) Examine the firing spring and see that it is in good condition. Assemble the firing spring in the guide tube.
(h) Assemble the firing plunger in the guide tube. To do this, slide the firing plunger sleeve on the firing plunger, depress the release plunger so the balls can recede, then slide the sleeve over the balls. With the sleeve in place, push the firing plunger into the guide tube and continue pushing the firing plunger until it is in the cocked position. As it is possible to start the firing plunger in backwards, care should be taken to see that the firing point points outward toward the detonator holder.
(i) Replace the detonator collar, detonator holder, and detonator holder locking spring.
(j) Clean the depth markings on the flange so they are clear. See that the two holes in the inlet valve stop are clean and open.
(k) Test the pistol as directed in the instructions for testing pistols.
(l) If the pistol fails to function satisfactorily, examine the assembly to see if the trouble can be located and corrected. If the pistol cannot be made to function satisfactorily, mark the pistol "unsatisfactory" and set it aside for complete overhaul or, if aboard ship, return it to a depot for replacement.
23. Inspection and overhaul of booster extenders.--
(a) Test the booster extender as directed in the instructions for testing booster extenders. If the booster extender passes this test satisfactorily it is ready for service use.
(b) If the booster extender fails to function satisfactorily and the trouble cannot be located and corrected without disassembly, mark the booster extender "unsatisfactory" and set it aside for complete overhaul or, if aboard ship, return it to a depot for replacement.
24.Inspection of booster cans.--
(a) Inspect the booster can for leaks, holes, or any evidence that the TNT charge is wet.
(b) Examine the booster for deformations which might prevent its free movement inside the depth charge central tube. Examine the joint between the can and head and see that it is made up tight and in good condition.
(c) Depots shall provide themselves with a ring gage to be used in gaging the loaded booster cans. This gage shall have an inside diameter of 4.145 inches (plus 0.000, minus 0.003), and a length of 1.0 inch (plus or minus 0.030). The booster cans shall pass freely through this gage.
(d) Inspect the detonator envelope and see that it is in good condition and is securely soldered in the booster can.
(e) If there is any indication that the .booster is defective, set the unit aside for complete overhaul or, if aboard ship, return it to a depot for replacement.
Preparation of Depth Charges for Firing
25. General instructions.--Prepare depth charges for firing only from material which has passed the routine inspection and overhaul indicated in paragraphs 20 to 24, inclusive. Make a check-off list and use it during the preparation for firing.
26. Assembly of the booster can and booster extender in the case.--
(a) Engage the socket on the booster head with the connecting collar on the booster extender. Assemble the booster and booster extender in the case, using a good gasket.
(b) Fit the bolts and lock washers. Use the socket wrench supplied in the testing sets and tighten the bolts uniformly so as to make a good watertight joint between the booster flange and the case. It is a good plan in bolting up a joint of this kind to tighten all bolts until a light tension is taken on each. Then tighten one bolt a little more and then the one next to it, and so on, progressing around the flange in one direction until the bolts are all uniformly tight.
(c) Test the booster extender for freedom of motion. To do this remove the safety fork and engage the extender testing tool with the booster spindle. Push the tool inward about one inch and observe if the spindle and booster move without pronounced binding. The spindle has a certain natural resistance to motion due to the reaction of the spring and the friction of the locking balls. If there is binding or resistance in excess of this natural resistance, examine the assembly for the cause, which should be located and corrected before proceeding with the assembly.
(d) Put a plain safety fork in place. Use the hook on the extender testing tool to retract the booster spindle so that the fork can be entered in the groove in the spindle.
27. Assembly of the pistol in the case.--
(a) Inspect the holes in the inlet valve stop, to insure that they are clean and open.
(b) Set the index pointer on SAFE. Use the depth setting wrench as it will facilitate setting the index pointer.
(c) Release the detonator holder locking spring and remove the detonator holder and detonator collar. See that the pistol is cocked. If it is not cocked, cock it, using the cocking tool.
(d) Mount the detonator in position between the detonator collar and detonator holder. Replace the detonator holder locking spring. The point of this spring should show on the inside of the guide tube between the detonator holder and the end of the tube. If the detonator holder interferes with the point of this spring it indicates that the assembly is not correct. Determine the trouble and correct it before continuing the assembly.
(e) Assemble the pistol in the case, using a good gasket.
(f) Fit the bolts and lock washers (see the instructions contained in paragraph 26 (b) relative to tightening the bolts). (g) Install a plain inlet valve cover.
28. General instructions.--The complete overhaul and repair of depth charge material is to be undertaken only by authorized shore stations.
Chapter 10. DEPTH CHARGE RACKS
1. The depth charge rack holds one Mark 6 depth charge. The rack consists of a base which bolts to the deck, and on which are mounted two tracks. A double securing strap passes over the depth charge, holding it to the tracks on which it rests. A quick release mechanism secures the strap at the inboard end.
2. The base of the rack is made of sheet steel. At each end of the rack base is a flange with bolt holes by which the rack is secured to the deck. Mounted on each end of the rack base is a single track, made of angle steel, with the toe of the angle down and in. The depth charge rests on these two tracks, and is prevented from sliding fore and aft by the upright legs of the angles. The tracks slope downward and outboard. The inboard end of the tracks curves sharply upward to form a shoulder against which the depth charge is secured.
3. The securing strap secures the depth charge to the rack. The strap is a single galvanized steel cable, both ends of which are connected by a triangular link. The strap is held on the outboard side of the rack by two adjustable screws and pulleys, one at each end of the rack. The straps pass over the depth charge and the triangular link is held by the quick release mechanism. The purpose of the adjustable screws and pulleys as the outboard securing points for the strap is to tighten the strap around the depth charge. (See figs. 22 and 23.)
4. The triangular link is secured by the release hook of the quick release mechanism. The release hook is tilted inboard by the toggle lever in order to release the link and securing straps. Until the depth charge is to be released, the release mechanism is locked by a safety pin which passes through the toggle lever. A safety fork prevents the safety pin from backing out accidentally. All parts are brass or noncorrosive metal. The safety pin and fork both have a short chain to secure them to the rack to prevent their loss.
5. To secure a depth charge in the racks, the adjusting screws which serve as outboard securing points for the securing strap
are slacked off. The charge is placed in the racks, the securing strap passed over the charge, and the triangular link caught by the release hook. The safety pin locks the release hook in place, and the safety fork is clipped over the end of the safety pin. The adjusting screws and pulleys are now tightened to remove all slack in the securing straps.
Figure 22.--Type C depth charge rack. End view.
6. To release a depth charge, the safety fork must first be removed, then the safety pin. Then by pulling the toggle lever inboard, the release hook is moved inboard so that the triangular securing strap link is released, allowing the depth charge to roll overboard.
7. A lanyard clip is welded to each end of the rack. A lanyard may be secured to the safety fork or safety cover on the depth charge and secured to one of these clips. By this means the safety
Figure 23.--Type C depth charge rack. Inboard side.
fork and safety cover may be removed automatically as the charge rolls off the rack, making it unnecessary to remove them by hand.
8. The quick release mechanism, and adjusting screw and pulley mechanism, are made of brass or noncorrosive materials. However, they must be kept clean and in good working condition. They should not be painted. The rack itself is steel, and must be protected by a coat of paint to prevent corrosion.
Chapter 11. SMOKE SCREEN GENERATOR, MARK 2
1. The purpose of the installation is to provide means for laying smoke screens utilizing chemical smoke mixtures.
2. General.--The generator is carried on the stern of the boat, with all piping and accessory equipment secured to the carrier rack. It consists of one 35-gallon tank secured to an emergency release carrier, which in turn rests upon rollers in a carrier rack. The carrier is secured to the rack by a latch. Appropriate piping conducts CO2 from a CO2 bottle attached to the carrier rack to the tank. The smoke mixture is discharged from the tank through piping and out of two nozzles. The C02serves only as a source of pressure to force the smoke mixture out the nozzles as a spray. Maximum operating pressure of the generator is 150 pounds per square inch.
3. The 35-gallon GENERATOR TANK is fabricated from sheet monel metal, joined by welding. Within the tank are baffle plates to add strength and minimize surging, and a discharge tube which empties the tank as completely as possible by taking the liquid from the low end. On the outside of the tank are two reinforcing bands, which locate and restrain the tank in its mounting; a filling fitting; a flange for the smoke line connection; a pipe-threaded CO2 inlet tube; and two pad eyes.
4. The tank is mounted in two SADDLES which are welded to the emergency release carrier. Each saddle contains a pair of rollers, upon which the tank may be rotated into its proper position. The reinforcing bands locate the tank in a fore and aft position on the saddles.
5. The tank is secured in place upon the emergency release carrier by the TANK ANCHORING SLINGS. The slings are secured to cable anchor brackets on the carrier by clevis bolts.
Figure 24.--FS smoke screen generator.
6. The EMERGENCY RELEASE CARRIER is in effect a skid upon which is mounted the generator tank; the discharge piping and nozzles; and a part of the CO2 pressure lead. A latch on the forward end of the carrier rack secures the emergency release carrier in place. The latch lever is fitted with a toggle-pin which restrains the lever so that the generator cannot„be jettisoned unless the toggle-pin is first removed. The purpose of the emergency release carrier is to allow the generator tank to be jettisoned in case it has been hit.
7. GENERATOR CO2 piping may be traced on the diagram. Starting at the CO2-bottle, the generator piping consists successively of a CO2 bottle and valve; a section of copper piping from there to a variable reducing valve; a length of piping from the reducing valve to slip joint, and then to the inlet valve on the tank. The maximum working pressure on this system is 120' pounds. The slip joint serves as a connection between the stationary piping secured to the carrier rack, and the piping which is secured to the emergency release carrier and tank.
8. GENERATOR SMOKE LINE may be traced on the diagram. The line leads from the after, lower end of the tank to the forward end of the tank; out through the outlet valve; then aft below the tank to the two spray nozzles over the stern.
9. SPRAY NOZZLES are intended to emit the smoke mixture in finely divided form, the resulting spray to form a comparatively wide cone. Nozzles are made adjustable, in order to obtain the optimum spray, but the adjustment once determined is not intended to be altered in service except to reestablish the original setting. The nozzles should be pointing aft and up at an angle 0f about 45° above the horizontal.
10. Filling caps are provided for each tank. They are intended for use only when tanks are to be filled with smoke mixture, or when, having been discharged, tanks are to be flushed with water. Under normal operating conditions, a filling cap should never be opened unless the tank is known tohave been completely discharged, and then only while observing all safety precautions noted in paragraph. 17.
11. The CARRIER RACK is the frame in which the emergency release carrier is normally mounted. It is designedly slanted outboard (i.e. toward the stern) at an angle to permit
jettisoning the generator by gravity. It contains eight rollers whose axes are horizontal and approximately athwartships, upon which the emergency release carrier rests, and six rollers with vertical axes to restrain the emergency release carrier from sidewise movement.
12. The RELEASE MECHANISM permits the generator to be jettisoned in case of an emergency, such as rupture of a full tank by gunfire or by collision, or in case of fire near the generator. Jettisoning may be accomplished by first removing the toggle pin from the emergency release lever, and then pulling the lever forward, away from the tank. Gravity will cause the emergency release carrier to roll aft on the carrier rack rollers and over the stern. The slip joint in the CO2 piping automatically disconnects when the release carrier moves aft.
13. In general, the care of the smoke screen generator equipment involves inspection and maintenance as required to insure that the equipment is at all times in serviceable condition. Periodic inspection should be performed to check up on the following points:
(a) That all working parts are properly lubricated.
(b) That all working parts are in operable condition.
(c) That no leak either of air or smoke mixture exists.
(d) That no parts are corroding.
(e) That there is no accumulation of paint, dirt, or other material on an emergency release carrier inboard of any of the rollers mounted in the carrier rack, or between the holding-down keys on the emergency release carrier and their mating parts on the carrier rack, which might possibly impede the jettisoning of the generator in case of an emergency.
(f) That all paint is in good condition.
14. Corrosion of the generator tanks, and of the piping, valves, nozzles, etc., carrying smoke mixture, is hot expected to develop under normal conditions except after considerable periods, since these parts are made of monel metal. CO2 piping and valves, rollers and axle pins, and cast parts are brass or bronze, and therefore are not expected to corrode seriously under normal conditions. The cables of tank anchoring slings are corrosion-resisting steel. The carrier rack, emergency release carrier,
and saddles are fabricated from common steel and therefore corrosion is normally expected to develop upon any part of the surface not properly protected by paint. Protection of the CRS cables of the slings is to be accomplished by the use of graphite lubricating grease. All of the materials of the smoke screen generator except monel metal may be expected to corrode rapidly if exposed to FS Smoke mixture.
15. The mounting of a generator, after original installation, should proceed as follows: The emergency release carrier is to rest upon the rollers which are mounted in the carrier rack, the carrier latching hook being engaged in the carrier latching eye and secured therein by a toggle-pin. The discharge tube, which passes through holes in the cradle, may be loosely in place. Before proceeding further, the proper lubrication of all rollers and other operating parts should be checked. The tank is now placed upon the rollers of the cradle which are part of the release carrier, the rollers being at the center of the reinforcing bands, and the tanks are rotated upon the rollers until the rollers engage the machined recesses in the bands. The tank anchoring slings are now checked for proper protection against corrosion and are installed so that the cables straddle the reinforcing bands of the tank. Make up the CO2 and the smoke discharge pipe connections. Tighten tank anchoring slings.
To dismount a generator, proceed as above but in the reverse order.
16. The FILLING OF TANKS will be performed on board a tender or ashore. Filling requires the provision of a sling arrangement such as indicated on plate III. The object is to transfer smoke mixture from the standard 55-gallon shipping drum to a generator tank without spillage and with the minimum of exposure of the smoke mixture to the atmosphere. The computed internal volume of the generator tank is 35.9 gallons, but its charge is only 32 gallons, to allow for expansion. The weights involved are about as follows:
Pounds Generator tank (empty) 125 Shipping drum (full) 900-1000 Filling equipment 16
The following procedure is suggested for filling:
(a) Secure slings, the drum and tank lying on deck or on a platform, the bung of the drum being up.
(b) Remove tank filling cap and install filling gage, first making sure that the filling gage float is free and will register when the tank is filled. Keep the float stem oiled lightly where it protrudes through the filling gage retaining nut.
(c) Make sure that the air and discharge stop valves on the tank and the plug cocks in the filling and vent hoses are closed.
(d) Make sure that the gasket of the filling and drain drum connection is in place and in good condition and is coated with soft deflocculated graphite lubricating grease.
(e) Remove the screw cap from the bung of the drum and install the filling connection on the drum. Loosen the screw cap cautiously and allow the drum to vent, if necessary, before removing the cap entirely.
(f) Connect the filling and vent hoses to the generator tank first making sure that the ball check valve has been removed from the air-line stop valve. (The drum may be rolled over to facilitate these connections.)
(g) Hoist drum and generator tank so that the tank stands vertically and the drum hangs with its axis horizontal, with the bung down, taking care that no strain is put on the filling or vent hoses.
(h) Open the two stop valves of the generator tank.
(i) Open the plug cock in the filling hose cautiously. If any water is present in the tank, a reaction of some violence may be expected, and smoke may be emitted from the orifice around the stem of the filling gage on the tank. If a reaction occurs, close the plug cock immediately. Do not open again until all reaction ceases, and then with the same caution as before.
(j) Open the plug cock in the vent line cautiously.
(k) Permit the liquid to flow while watching the filling gage vigilantly. "When the filling gage stem starts to rise, shut the plug cock in the filling hose immediately. Failure to do so may result in the entrapment of smoke liquid in the filling line between the generator tank stop valve and the filling line plug cock, and in its subsequent spillage. Also. the tank should never be filled beyond the 32-gallon limit, which the gage is designed to indicate, as sufficient space must be left for possible
Figure 25.--FS generator. piping diagram.
expansion of the liquid in ease the filled tank is later subjected to a considerable rise in temperature.
(l) After an interval of a few seconds, close the vent hose plug cock. Disconnect the vent hose from the generator tank, leaving the tank valve open to vent the tank. Cautiously break the joint between the filling hose and the generator tank, allowing any liquid which may be entrapped to drain into the tank. After completely disconnecting the filling hose, close both generator tank valves.
(m) Remove filling gage and replace the tank filling cap, making sure that its gasket is in place and in good condition, and coated well with soft deflocculated graphite lubricating grease. If the filling gage is not to be used again immediately, immerse in sodium bicarbonate solution, rinse in fresh water, and wipe dry.
(n) Remove any smoke mixture which may be present on the tank connections. As much as possible should be wiped up with dry cloth or waste (discarding immediately). Sodium bicarbonate solution may then be applied, taking care that none is allowed to remain where it may later contact smoke mixture, since such contact will produce a relatively insoluble white precipitate. Lower the generator tank. Lower the shipping drum, with the bung up, disconnect the filling and vent connection from the drum, and replace the screw cap on the drum. Wash the drum around the bung with sodium bicarbonate solution followed by water. If the filling equipment is not to be used again immediately, open both plug cocks and wash thoroughly. Sodium bicarbonate solution may be used if entirely removed afterward by rinsing with water.
(o) In partially filling a tank from a partly empty drum or in completing the filling of a tank from a second drum, the same procedure should be followed as when completely filling a tank from a single drum, except that any water present in a tank will be spent by the first-smoke mixture entering.
17. The following PRECAUTIONS are to be observed while filling tanks from drums or while otherwise handling smoke mixture:
(a) The standard smoke mixture is FS, a liquid compound of sulphur trioxide and chlorosulphonic acid. It combines immediately and violently with water (even with atmospheric
moisture), the products being sulphuric and hydrochloric acids in the vapor state. In general, then, the precautions are those necessary in the handling of strong, fuming acids, with the additional requirement that moisture must not be permitted to contact the smoke mixture except (as when cleaning up spillage) in such large quantities as will immediately complete the chemical reaction, dissipate the resultant heat, and dilute and flush off the resulting acids.
(b) All personnel handling FS will wear acidproof clothing or aprons, gas masks (since the smoke, although nontoxic, will burn the respiratory system if breathed in high concentration), rubber gloves and rubber boots. Personnel not so protected will stand clear and to windward. Every precaution should be taken to prevent liquid FS from contacting any part of the body.
(c) If FS liquid does get on any part of the body, it will immediately start to combine with body moisture and will cause a severe burn unless immediately removed. Since the application of water intensifies the reaction, as much as possible of the liquid should be wiped off with dry waste or cloth if available. Then flush off immediately and thoroughly with a large quantity of water, followed by washing with a weak solution of sodium bicarbonate in water. The application of grease in any form before thorough cleaning as above will cause the burn to be progressive and to penetrate into the body tissues.
(d) If liquid FS in any but the smallest quantity gets on any garment, remove the garment immediately. Do not apply water while the garment is on the body, as severe burns may result. Wash the garment with a hose or rinse it in a large container of water; then soak it in a saturated solution of sodium bicarbonate, afterward removing the carbonate solution by a fresh water rinse.
(e) Except as noted in the two preceding paragraphs, spilled FS liquid should be immediately drowned by hosing, taking care to avoid the droplets which may be spattered around by the reaction of FS with water. If this wetting-down is performed in an area used for filling operations, the area should be dried before any further tanks are filled.
(f) FS liquid in drums should be stowed under shelter and not adjacent to any boiler, radiator, steam pipe, etc. FS of itself is not a fire hazard, but when spilled on other material
constitutes the same hazard as concentrated sulphuric acid, in addition to its fumes. While in store, a drum should be vented occasionally by loosening but not removing the bung screwcap while the bung is up. If considerable pressure has built up in the drum tested, all drums should be vented. This venting should be performed in the open air, by personnel protected as prescribed in paragraph 17 (b).
(g) Filling operations should be conducted in the open air, preferably under cover, but in all events in a dry location protected from spray. The drums should not be exposed to direct sunlight before opening, since a vapor pressure may be built up which will result in a dangerous spurt of FS when the bung is opened. The location chosen for filling operations should he such that the wind blows away from any adjacent personnel or material (including ship's structure).
(h) Since the smoke-producing reaction of FS occurs with water, generator tanks and all filling equipment should be thoroughly dried before commencing filling operations. The agency performing the filling operation is charged with the proper washing of generator tanks with fresh water, and with their subsequent thorough drying, which should be accomplished by moderate heating. Generator tanks, as received from the vessels rising them, should have been thoroughly flushed with fresh water.
(i) Filling equipment, after use, should be thoroughly washed in fresh water whenever it is not to be used again within 1 hour. After each washing, it should be thoroughly dried by moderate heating.
(j) Filling hose should be periodically subjected to hydrostatic test at 50 pounds per square inch in order to detect any progressive deterioration which may occur over long periods.
(k) Shipping drums, if still serviceable, may be re-used. As soon as emptied, they are to be thoroughly washed out, dried, and returned to store.
(l) No attempt should be made to salvage the liquid in a leaky or otherwise defective generator tank. If practicable, discharge the tank as when laying a screen; if not, dump tank and contents overboard in deep water. If the defect is a minor one affecting only a tank fitting or attachment, the tank maybe salvaged, but no attempt should be made to salvage a tank having a structural defect.
Figure 26.--Refilling FS tank.
18. Operation of generators.--To lay a smoke screen the following operations are performed:
(a) Check to see that the reducing valve is closed, (i.e. valve handle backed all the way out--no pressure on valve spring).
(b) Open overboard discharge valve wide.
(c) Open CO2 cylinder valve.
(d) Open reducing valve to 40 pounds pressure.
(e) Open inlet valve wide.
(f) Open CO2 pressure to 75 pounds. If screen is not heavy enough, increase pressure, but never over 120 pounds. The optimum pressure will usually be in the range of 75 pounds to 90 pounds.
To shut off generator whether tank is empty or not empty: (a) Close CO2 inlet valve on tank.
(b) Close CO2 valve on CO2 bottle.
(c) Close overboard discharge valve.
19. (a) It is not desirable to retain a partially discharged tank indefinitely. If left with such a tank after a screening operation, and if it appears that no further screening operations will be conducted for some time, the tank should be completely discharged at the first opportunity in the same manner as in laying a screen, and should then be opened and washed out as described below.
(b) Upon the conclusion of a screening operation, empty tanks should be washed, as soon as opportunity offers, by inserting a fire hose nozzle into the "filling hole" of a tank filling as far as possible, with very little pressure, and then draining the tank. This should be repeated three times. As this is not practicable aboard an MTB, it should be done in an open area away from boats and buildings. This necessitates removal of the tank from the carrier and the disconnecting of the lines to the tank. This operation should not be undertaken unless the nozzleman is protected as required by paragraph 21 (b). When water first enters the tank a considerable reaction is to be expected; therefore proceed with caution and avoid spattering. The discharge line and nozzle must be flushed out thoroughly
(c) Upon conclusion of a screening operation, the entire boat's structure adjacent to tanks should be washed down with a hose. If practicable, the tanks should be washed out or re-
moved first, since some emission of smoke or spattering of liquid, or both, may be expected during washing.
20. Smoke-screen tactics.--See MTB Tactical Bulletin.
21. As the atomized FS smoke mixture leaves the nozzle of the generator, it combines with the moisture of the air to form finely divided fog particles. The heat developed by this chemical reaction causes the smoke screen to rise. Normally the screen will rise from 200 to 300 feet, forming a solid screen from the water to this height. One tank of smoke mixture may be expected to give a screen about 3,000 yards long. A number of shorter screens may be obtained, the number depending on the length of the shorter screens.
Chapter 12. FM SMOKE GENERATOR
The FM or "Elco" smoke generator consists of a steel bottle of the type in which commercial gases are contained. It has a single threaded opening at one end, which is controlled by a valve. This valve is part of the bottle assembly, and the wrench that opens it is furnished with the original bottle (or generator) of smoke. This wrench has a hinged handle so that a steel protective cap may be screwed onto the bottle over the valve assembly with the wrench attached when the generator is not in use.
To spray the smoke liquid from the generator, a smoke pipe is furnished. This pipe is about two feet long and is bent slightly. On the lower end it carries a fitting to connect the pipe to the nipple on the generator valve assembly. A hinged wrench for this fitting is clipped to the smoke pipe. At the upper end the pipe is threaded to receive a single nozzle.
Four nozzles are provided, and are quickly interchangeable. They are marked for 3 min., 5 min., 8 min., or 12 min.; the time the smoke will last in a continuous screen, using the respective nozzle. The 8 min. nozzle is for use under average condition and the 12 min., nozzle is for night use. If the weather is very windy either a 3 or 5 min. nozzle would produce a better screen.
The generator is carried athwartships on the stern of the M. T. B. There are two small wooden cradles secured to the deck, and the bottle is secured to the deck by two flat steel straps which pass over it.
NOTE.--The valve end of the bottle must be slightly lower when installed. The exhaust line leading from inside the bottle to the valve is a short, curved pipe that extends to the side of the bottle just below the valve. Also, it is necessary to install the bottle with the nipple fitting for the smoke pipe pointing straight up, so that the exhaust line opening is at the lowest part of the bottle.
PRINCIPLE OF OPERATION
The smoke-producing liquid in this generator is carbonated when the bottle is filled; thus it is under pressure and will be faced out of the bottle when the valve is opened. No additional source of pressure is required. This generator is built on the principle of a seltzer bottle. It can not be refilled except by the manufacturer so a new bottle of smoke must be installed when one is emptied.
The liquid that produces the smoke is titanium tetrachloride, which, when sprayed into the air, combines with the moisture in the air to form hydro-chloride acid and titanium hydroxide, thus forming smoke. The liquid is very corrosive on steel or flesh. Burns from FM are to be treated in the same way as FS burns.
To lay a smoke screen the smoke pipe must be attached with the appropriate nozzle covered with a rubber cap to keep salt water out. The valve in the bottle is opened fully. To stop smoking, the valve is closed and a rubber cap placed over the nozzle to replace the one blown off when the valve was opened. Only use as much smoke as is needed for the occasion. Save the rest for another time.
As soon as possible after laying a screen remove the smoke pipe and flush it out thoroughly with water. Wash down the deck and generator with water.
Avoid getting the liquid on the skin or clothing. It burns like a strong acid. Treat burns the same as FS burns.
Keep nozzles, smoke pipe, and valve assembly clean and lightly oiled. Be careful not to crossthread brass couplings. Do not force valve closed beyond normal tightness. The liquid in the upright smoke pipe will cause a streamer of smoke after the valve is closed, leading one to believe the valve is not seated. Forcing the valve will score the valve seat, thereby causing it to leak.
Notes on Torpedoes
1. Included in these notes are certain check-off lists for preparation and upkeep which are the result of the operating experience of several squadrons.
2. It will be found that certain parts of the torpedo are subject to more deterioration under motor torpedo boat operations than in other types of vessels.
3. Among the first of the above casualties is corrosion from continuous wetting and entrance of water in the tube around the head. This can be remedied by packing around the head tightly with heavy grease and also by slushing the inside of the tube with a mixture of a heavy grease and hot running oil. This forms a sort of bond and tends to prevent water entrance. If the grease used around the head is a heavy grease and is continually repacked, in a short time it will be impossible for water coming over to wash it out.
4. Due to continuous dampness there is considerable trouble with corrosion of exploders, wet boosters, and detonators. These should be inspected at least once every week. Exploders must be kept in good condition.
5. Gyros are subject to considerable vibration and hence damage. Pivots and bottom bearings become grooved and pitted or scratched. Gyros also pick up considerable moisture, and corrosion proceeds rapidly if not noted and checked promptly. They should be checked at least every other week.
6. The usual leaks that develop are predominantly those due to vibration. Stop valves and starting piston plugs should be checked every few days for leaks. The next most common leaks are forward air flask bulkheads and starting pistons. It cannot be stressed too highly that all leaks must be located and stopped as soon as they are indicated. In this connection, torpedoes should be gaged every other day and a running record kept. They should be gaged at the same time each day to have com-parable
temperatures and therefore pressures. Any big drop must be investigated immediately.
7. Limited storage facilities and operating conditions make the conditions of impulse charges at all times subject to considerable doubt. They should be inspected weekly for bulging or swelling of wadding indicating excess moisture.
8. Appended are recommended check-off lists.
Routine Upkeep of Torpedoes
A. Three times weekly.
1. Gage and boost air flasks as necessary. Gage at same time each day. Keep running record.
B. Twice weekly.
1. Open tripping latch and inspect for leaks around starting piston plug.
2. Inspect for leaks around charging check and stop valve.
1. Raise tube tripping latch.
2. Open tube door and put on propeller lock.
3. Remove flat nose piece from warhead and install nose ring.
4. Train tube in line for loading and place three dollies on scribe marks on deck.
5. Close stop valve and place wedge behind starting lever.
6. Attach tackle to nose ring and haul torpedo out of tube.
7. Break igniter lead.
8. Remove propeller lock and turn propellers 50 turns.
9. Operate depth mechanism from 0 to 50 and return to required setting.
10. Refill oil tanks.
11. Take out igniter and inspect combustion pot. Excessive alcohol and water is a sign of leaks.
12. Open stop wide and turn back one-eighth turn. If excessive "carry over" occurs, drain pot. If a blast goes through, it may be necessary to relock gyro also.
13. Reinstall igniter, make lead.
14. Reload torpedo in tube.
1. When making weekly check, remove exploder, detonator, and booster, and check for evidence of moisture.
2. Check gyro for rust, excessive oil.
1. Remove torpedo from tube as in weekly routine.
2. Disconnect and remove igniter, note condition of end seal.
3. Remove one afterbody; and tail drain plug and drain.
4. Turn torpedo 180 degrees draining combustion flask on way over.
5. Remove exploder mechanism and detonator:
(a) Remove holding screws and cover plate over exploder mechanism base.
(b) Remove holding screws and exploder mechanism with detonator attached.
(c) Remove detonator from exploder mechanism and place in safe stowage space.
6. Remove booster from casing and place in safe stowage space.
7. Replace cover plate and holding screws.
8. Turn torpedo right side up.
9. Remove air, fuel, and water check valve plugs, work and oil check valves, replace plugs.
10. Remove strainer plugs; remove and clean air, fuel, and water strainers and replace; replace strainer plugs.
11. Remove port hand hole plate.
12. Remove safety stick and throw starting lever to rear by hand. Rotate starting gear index spindle several revolutions, insuring that starting piston seats. Replace starting lever wedge.
13. Operate depth setting mechanism from 0 to 50 and return to required setting.
14. Work horizontal rudders a few times up and down by hand, using one hand on each rudder, with the same amount of force on each.
15. Work vertical rudders by hand using same method.
16. Remove propeller lock, turn propellers by hand at least 50 times. Listen for unusual sound. Check action of pallet and slide to see that pallet does not engage pallet pawls while in neutral position with gyro locked.
17. Replace propeller lock.
18. Oil and grease power plant.
(a) Fill oil tanks (B).
(b) Remove grease packing screw from end of after propeller shaft, use grease gun and fill till bearing will take no more (G), replace grease screw.
(c) Fill bearing in afterbody with oil (B).
(d) Fill grease cavity in forward propeller with grease (G).
19. Remove gyro clamp plate cover and unlock gyro by hand.
20. Remove gyro bottom head.
21. Remove, inspect, and oil gyro. Note that balance nut is tight.
22. Lock and unlock spinning mechanism, by hand and by rotating spinning shaft.
23. Turn gyro index full range right and left. Note that index inside pot lines up with outside setting.
24. Remove propeller lock and turn propellers till cam pawl is in extreme forward position.
25. Install gyro and gyro bottom head, lock gyro, replace clamp plate cover and gasket.
26. Replace port hand hole plate, afterbody, and tail drain plugs.
27. Gage and boost airflask as necessary.
28. Fill fuel and water compartments.
Preliminary Adjustments for Mark VIII-3C and 3D Torpedoes.
These adjustments assume that the torpedo is in good condition mechanically (not in need of major overhaul) and is to be prepared for further firing.
1. Overhaul the tail; remove tail cone; clean and lubricate all parts therein; examine propellers and remove dents; test exhaust valves for condition of springs; see that sinking gear is removed (installed for war shot) ; reinstall all parts and cone.
2. Turn propellers over by hand to see if shafting is properly assembled and that all parts turn freely; put propeller lock on.
3. Verify condition of exercise head (fill and blow down on deck) ; secure in place on flask and make the air blow connection.
4. Fill oil tanks, oil cups, oil tail bearing, and prime oil pump.
5. Rotate distance index till starting piston seats, noting position near zero when starting piston seats (listen for the click when the distance trip releases the stop plug).
6. Remove atmospheric chamber under diaphragm of depth mechanism. Examine diaphragm for condition, replace if necessary (depth spring should have no load during this operation) ; reinstall atmospheric chamber.
7. Place safety wedge behind starting lever.
8. Remove fuel- and water-filling plugs.
9. Install charging line (use safety strap) and charge torpedo to 1,500 pounds; remove charging line and close stop valve.
10. Remove, examine, and clean air strainer.
Prepare for test of rudder throws.
11. Connect low-pressure testing line in line from charging valve to air strainer body, tool No. 223 in strainer body.
12. Set up on reducing valve speed screw (speed ring in place).
13. See that transportation screw is in place, remove afterbody hand-hole plates, gyro clamp plate and strainer; disconnect steering engine air leads; put in a few drops of gyro oil in the air nipple to oil the engines; reconnect the air leads.
14. Open stop valve and with low pressure air (400 pounds gage) proceed as follows:
(a) Check alignment of horizontal rudders with zero lines on cone.
(b) Remove transportation screw.
(c) Level torpedo.
(d) Remove test plug from atmospheric chamber in depth gear. Place 16-pound weight on depth spring (screw rod to nut and hang weight on it).
(e) Turn depth index until marking on depth engine valve stern indicates mid travel.
(f) Move pendulum fore and aft a few times and note if valve comes to rest in proper position.
(g) If depth index does not read "ten feet" set it by disengaging spring sleeve from socket. Upon completion be sure spring sleeve fully engages socket again; turn spring slightly if necessary.
(h) Set depth index on zero and remove test weight.
(i) Replace test plug and make sure the washer is in good condition.
(j) Swing the pendulum by hand all the way aft and all the way forward. Read the up and down rudder throws when the pendulum is against its stops and adjust the horizontal rudders so the throws will agree with the record book 1U 4 D for this torpedo.
(k) Move the gyro steering engine valve and read the rudder throws using tool No. 44; the throws should agree with the record book.
(l) Note that air is blowing through the top bearing extended over the gyro pot, for the air sustained gyro.
15. Close stop valve, remove testing set with tool No. 223.
16. Replace charging valve plug and washer, also air strainer and plug.
17. Replace water compartment filling plug.
Prepare to test for proper gyro control.
18. Crack stop valve.
19. Put in transportation screw and turn torpedo upside down.
20. Note that gyro outside setting socket is on zero, also gyro pot itself.
21. Now release the spinning gear and turn the pot 90° right and 90° left from the outside setting socket to insure there is no interference in the afterbody; return to zero and check again for aid position.
22. Remove bottom plate on gyro pot. Clean and dry inside of pot.
23. Lock and release spinning mechanism to limber it up.
24. See that cam pawl is in the extreme forward position and install gyro (if the pawl is not forward, cautiously remove propeller lock, turn propellers until it is, and replace propeller lock).
25. Lock and unlock gyro by hand a few times. Each time carefully examine the finger trip to see that it is against the pot wall; if not, the gyro is not fully locked, so release the spinning gear and turn it by hand about 11/2 revolutions clockwise viewed from aft, when it should be possible to fully lock the gyro (as indicated by the finger trip being against the pot wall).
26. Place gyro engine valve in approximately mid position by hand. Remove propeller lock cautiously and turn propellers
by hand, watching the gyro engine valve meanwhile. If the valve moves, the gyro pot is not properly indexed for a straight shot. It should be properly centered' by the outside setting socket, noticing the resulting discrepancy. Report this to torpedo officer.
27. Take advantage of this opportunity to examine all piping in the afterbody for leaky condition.
28. Replace air screen and clamp plate. Be sure nothing has been accidentally left in afterbody and put on hand hole plates.
29. Turn torpedo right side up and put on a second propeller lock. Lash both securely.
30. Sling and hoist torpedo so it can be turned at will in the air while the gyro engines are running on the test to follow.
31. Fix centering marks on deck for noting creep of gyro on test to follow (remember that the ship itself may swing during the test.)
32. Remove safety wedge from behind starting lever and with stop valve closed and distance index off zero, throw starting lever to the rear. Open stop valve smartly, thus spinning gyro.
33. Close stop valve and remove propeller locks.
34. Keep clear of propellers and open stop valve sufficiently to operate vertical steering engines and main engine by air.
35. Swing the torpedo in azimuth and note operation of vertical rudders by the gyro as the torpedo is swung from side to side.
36. When satisfied with the test, close stop valve and put on propeller locks and lash securely.
37. Remove transportation screw.
38. Open stop valve sufficiently to operate depth engine.
39. Tilt torpedo alternately above and below the horizontal about 3°. Rudders should begin to move with 1/20 inclination.
40. Close stop valve and replace safety stick behind tripping latch.
41. Lower torpedo on truck or rack.
42. Put in transportation screw and turn torpedo upside down.
43. Remove gyro, replace bottom plate, air screen, and clamp plate.
44. Remove plug from afterbody siphon (install for war shot).
45. Turn torpedo right side up and replace fuel and water filling plugs.
46. Remove and oil all check valves and test operation by hand.
47. Slack up on speed screw.
48. Remove fuel and water strainers and blow through by mouth. Now do the same with a strainer known to be good; a clogged strainer will be detected at once by this method.
49. Check up on all joint screws to see they are properly set up.
50. Set up on after propeller shaft locking nut.
51. If exercise head is fitted with screwed torch pot rings, see that ones for use with torch pot are drilled for wiring.
52. Check up on securing of all accessible studs, nuts, and fittings.
With the above adjustments made, the torpedo is now ready for final adjustments.
Final Adjustments Mark VIII-3C and 3D Torpedoes
1. Propeller lock on.
2. Distance gear on zero.
3. Remove fuel and water filling plugs.
4. Charge to required pressure.
5. Fill head (exercise shot).
6. Drain air flask.
7. Cock air-blowing device, and test air-blowing head device for tightness (exercise shot).
8. Cock air-blowing device, open flask stop, and secure mechanism in head. See air-blow device washer properly on seat and follower ring screwed down tight (exercise shot).
9. Drill torch case ring for wire, do not use wedge. Insert torches in place, puncture top 1/8-inch hole (exercise shot).
10. Oil reducer.
11. Note speed ring. Set up on speed screw.
12. Examine air strainer--do not oil.
13. Crack stop valve.
14. Roll torpedo 180°.
15. Examine fuel and water strainers.
16. Oil and work check valves.
17. Renew diaphragm (note diaphragm should be renewed before every shot).
18. Replace drain plug and transportation screw.
19. Remove cover plate, air screen, and bottom plate, wipe inside of pot clean and dry.
20. Note gyro index on zero.
21. Inspect pallet pawls, see that they are clean and free.
22. Lock and release spinning mechanism.
23. Turn propellers by hand until pawls are in the extreme forward position when gyro is installed.
24. Install gyro, lock gyro, remove hand hole cover, place gyro engine valve in mid position; turn propellers by hand and watch engine valve; if valve moves, gyro is not correctly placed for straight shot. (Put gyro in position by angle setting device so pallet blade is in mid position; i.e. when it goes back and forth without shifting valve from mid position).
25. Unlock and lock gyro to insure locked gyro; enter hand hole plate and push locking bar home as far as possible. See afterbody siphon pipe and oil pipes clear of spinning gear for curved shot. Take out gyro.
26. Secure gyro cover with air screen and bottom plate in place.
27. Inspect gasket and replace hand hole cover.
28. Turn torpedo upright.
29. Fill oil tank and cup and prime oil pump.
30. Fill water compartment partially.
31. Fill fuel tank.
32. Advance fuel to sprays and replace fuel plug.
33. Fill water compartment, and replace water filling plug.
34. Dummy igniter out.
35. Turn torpedo 90° left; drain combustion pot.
36. Turn torpedo upright.
37. Set depth index.
38. Set distance gear off zero.
39. Crack stop valve.
40. Above completed, haul torpedo to dock. Put on warhead.
41. Inspect and install igniter and make connection.
42. Sinking attachment on. Replacement screw in.
43. Put in gyro. Lock and set angle.
44. Place dollies on deck and set by height gage if available. Otherwise by eye and adjust as torpedo is set in place.
45. Set torpedo on dollies. Put nose line on and take turn on cleat. See that tripping latch is open.
46. Push torpedo in tube till propellers are even with tripping latch.
47. Put in exploder, etc., as per warhead check off list.
48. Push torpedo into tube, being sure tail bearing slides into guide. Stop torpedo when it still has about six inches to go.
49. Take off propeller lock. Close tube door.
50. Push torpedo in till it bumps door.
51. Put in stop pins.
52. Take out safety stick. Close tripping latch.
53. Open stop valve wide and turn back one-eighth turn.
Preparation of a War Head for a War Shot
NOTE.--Before installing war head on the torpedo, it will be necessary to remove the following parts from the forward end of the air flask: (a) Pipe and clip from blow valve to exercise head.
1. Before installing war head on torpedo, turn upside down and thoroughly clean out the exploder housing with kerosene, allow to dry thoroughly.
2. Thoroughly clean gasket seats so gasket will seat on clean metal. This is of great importance!
3. Turn war head right side up and install on air flask, torpedo being horizontal, using only the screws provided with the war head.
4. Replace nose ring by flat nose piece provided, and set up securely.
5. The torpedo being otherwise ready for inserting in tube, take exploder mechanism from box and carefully examine base plate seat to make sure it is absolutely clean.
6. Inspect exploder mechanism to insure all parts are in efficient operating condition and place the mechanism in the unarmed condition. In the unarmed condition, the firing pin guide is cocked (tongue gripped by triggers), and the upper surface of the arming screw is flush with the upper surface of the arming screw nut, bench marks in line. The safety posts of the arming screw should make near contact with the trigger plate and should positively prevent separation of the lower legs of the trigger when the above condition exists.
7. Remove live detonator from detonator box and be extremely careful in handling the detonator so that it will not be dropped or struck. This is vital, and the safety of the ship is seriously involved in this and subsequent steps of preparation.
8. Remove container from detonator and inspect to see that the safety chamber and detonator are clean and in condition for satisfactory operation. Wipe off parts with clean dry rag as necessary. A drop of gyro oil should be wiped on detonator holder threads and no lint or other foreign particles left on any of the mating parts.
9. With detonator holder assembled in safety chamber and top face of detonator holder flush with top face of safety chamber (bench marks in line), attach assembled detonator to arming screw nut with screws provided in exploder box (glass jar). Use screw driver from exploder box so screws will not be injured. (Note particularly that guide posts of exploder mechanism are inserted through holes in rim of detonator holder.)
10. Remove tetryl booster from its container and storage box and see that casing is clean and free from foreign matter.
11. Take assembled exploder mechanism (fiber washer in place on exploder mechanism base) and securing screws to the war head and place booster on top of safety chamber, holding by hand so it will not fall off.
12. Insert these units upward in exploder casing of war head, being extremely careful not to drop them.
13. See fiber gasket properly aligned and while holding the exploder mechanism firmly to its seat in the war head, insert securing screws and set up evenly and firmly all around (this joint must be absolutely watertight).
14. Install cover plate over exploder mechanism base and see that fan is turned so blades do not project beyond lower surface of war head (two of the three blades are staggered in manufacture so this can be accomplished--do not make more than one turn of the fan to accomplish this and always turn fan in direction it will be turned while torpedo is running in water).
15. Load torpedo in tube.
Treatment of Torpedoes After a Run--Mark VIII, Mod. 3C and D
To guard against deterioration, and to insure maintenance of torpedoes in condition for further firing, the following treatment is essential after a run.
1. Hoist in torpedo, place on truck, and close stop valve.
2. Put on propeller lock. Install transportation screw.
3. Remove torch pot from head.
4. Close valve on forward end of flask.
5. Remove air blowing mechanism from head, clean and stow away with tension on spring released.
6. Drain afterbody and tail cone, and leave out drain plugs.
7. Remove handhole plates in afterbody.
8. Fill oil pot, tail bearings, and afterbody oil cup, prime oil pump by turning propeller.
9. Remove fuel and water filling plugs.
10. Remove igniter and set depth at zero.
11. Turn torpedo upside down (drain water from exercise head, and fuel and water from their compartments; also drain the combustion pot from the igniter opening). Install dummy igniter.
12. Remove gyro clamp plate cover, and remove gyro (turn propellers as necessary to get cam pawls forward of cam so gyro can be withdrawn).
13. Dry out and oil with gyro oil the top bearing in gyro pot.
14. If gyro has been flooded, immerse in gasoline and blow off with dry air. Put a few drops of gyro oil on wheels, side and bottom and top bearings. The gyro should be broken down for careful examination of balls and ball races as soon as practicable. If not flooded blow off gyro with dry air, and oil as above.
15. Turn torpedo right side up. Put safety wedge back of starting lever.
16. Charge air flask to about 700 pounds pressure. Install water filling plug. Remove plug to air strainer, and put in a few drops of gyro oil. Replace plug.
17. With an oil gun and using hot running torpedo oil, lightly oil steel parts of gyro mechanism and distance gear.
18. Close stop valve, remove safety wedge back of starting lever, remove propeller lock, and stand clear of propellers.
19. Crack stop valve, and allow engines to turn over and circulate fresh oil through all oil passages in the power plant. Operate horizontal and vertical steering engines to lubricate valves.
20. Close stop valve, put on propeller lock, put safety wedge back of starting lever.
21. Remove water filling plug, and reinstall fuel and water filling plugs.
22. Slack back on speed screw on regulator.
23. Reinstall drain plugs and afterbody handhole plates.
24. Turn torpedo upside down; wipe inside of gyro pot dry. Replace clamp plate cover and washer.
25. Turn torpedo right side up.
26. Drain air flask.
27. Remove and oil check valves.
28. Reinstall fittings in exercise head for storage.
29. Prompt removal of the tail, and cleaning and lubricating of tail bearings, and prompt removal of the main engine from the afterbody and cleaning of salt water from between propeller shafts, are essential. These steps should be taken as soon as practicable after completion of a run, preferably within 36 hours, unless the torpedo is to be run again shortly, and these procedures are therefore impracticable.
Adjustments to Exercise Head Mk. 17, Mod. 2 for Mk. VIII, Mod. 3C and D. Torpedo
Tool No. 1. Remove air release mechanism 48-141A 2. Connect air blow lead to exercise head, blank off pipe in exercise head, crack air release mechanism stop valve and remove blank 13-141A 3. Attach exercise head to flask, take care not to crush pipe 49 4. Exercise discharge valves by hand, note that they operate and seat properly, and that the springs are not broken. 5. Fill exercise head with fresh water. 6. Calibrate air release mechanism to prescribed pressure 441; 34
Tool No. 7. Crack air release mechanism stop valve and blow through piping (note that there is no restriction in pipes) 49 8. Attach air release mechanism to air line in head 141A 9. Cock air release mechanism 441 10. Open air release mechanism stop valve. See valve is seated on its outboard seat 49 11. Test air release mechanism and connection for leaks by immersing in water. 12. With air release mechanism cocked, secure with leather gasket and cover plate, evenly in place 48 13. If no leaks are found around stem, put on air release mechanism protective cap. See washer in place and vent in cap clear 407 14. Install torch pot in torch case, using leather gasket; secure cover evenly in place. 15. Tear off seal on torch pot before loading torpedo in tube.
NOTE.----It is particularly important in preparing the exercise head for firing to be sure that the leather gaskets under the air release mechanism and torch case are tight. If they are not, the head may not blow and the torpedo will be lost.
Steps To Be Taken To Insure Against Cold Shots
Two--connections on line from reducer to air manifold.
Two--air checks' outer seat leaks and sticky valves.
Two--pipe connections (improperly set up, cross threaded, and closed-up orifice).
Two--bulkhead connections to fuel and water delivery checks.
Two--delivery checks (sticky and leaky).
Two--spray connections improperly made, crimped pipe, clogged sprays.
Two--igniter connections improperly made, cross threaded.
One--washer under plug in water compartment, set up tight.
One--reducer oil plug (not set up or cross threaded).
One--leaky syphon bellows in reducer.
POOR PIPE CONNECTIONS, LEAKY VALVES, CLOGGED STRAINERS, RATHER THAN DEFECTIVE IGNITERS, CAUSE COLD SHOTS.
Note.--PROPELLERS SHOULD BE BLOCKED, TAIL VANES TESTED FOR SQUARENESS.
Blowing head connections should be tested for 2,800 pounds pressure. Remove air blowing attachment and apply pressure to air blowpipe. Inspect inside of head for bubbles. An air leak at the nipple inside of head would cause a light head and a short run.
MAINTENANCE OF EQUIPMENT
PT's require considerably more maintenance than other types. Guns are subject to considerable wetting down and consequently greater upkeep. Appended are check-off lists for routine upkeep of guns and miscellaneous equipment.
The lists appended are as follows:
- Routine upkeep of 50-caliber.
- Routine upkeep of torpedo tubes.
- Check-off list for 50-caliber prior to firing.
- Points to be observed during firing of .50 cal.
- Points to be observed after firing of .50 cal.
- Casualty report for ordnance equipment.
- Routine upkeep of 20 mm.
- Check-off list for 20 mm. prior to firing.
- Routine upkeep of depth charges.
- Routine upkeep of Mk. 2 smoke screen generator.
MOTOR TORPEDO BOAT SQUADRONS
U.S.S. PT _____________________ Gun No. ______________________
Check-off list for routine upkeep of .50-caliber machine guns
Between firings, the following steps will be taken to insure maintenance of machine guns in good condition:
Gun covers will be kept on at all times when turret is not in use.
1. Inspect gun throughout without disassembly, for signs of rust or lack of oil. Carry out routine if gun has been wet or shows signs of corrosion.
2. Wipe all exposed parts with heavy oil, if needed.
3. Wipe bore and chamber with heavy oil, if needed.
BIWEEKLY OR AS NEEDED.
1. Disassemble gun.
2. Inspect, clean, and oil all parts using the "Before firing check-off list."
3. Reassemble, wiping all exposed parts with heavy oil and using heavy oil in bore, chamber, and outside of barrel.
Small arms: Rifles and pistols
1. Disassemble, inspect, clean, oil and reassemble.
MOTOR TORPEDO BOAT SQUADRONS
U. S. S, PT _______ Tube No. __________ For ________ quarter, 19 _____
Check-off list for routine upkeep of torpedo tubes
1. Grease training screw.
2. Clean training ways and lightly wipe with petrolatum.
3. Train tubes through limit of train.
4. Oil and operate dogs on door to prevent frozen threads.
5. Oil and operate wing nuts on stop pin plate.
6. Grease and operate tripping latch.
7. With gun, grease all pressure lubrication fittings:
On each pedestal (14).
On each door hinge (2).
On each tripping latch (1).
On each train screw bearing (1).
On each after train screw angle drive (2).
8. Paint all bare spots on tubes to prevent rust.
9. Check electrical firing circuit.
1. With torpedoes out of tube. Inspect and clean out impulse chamber and gas passage, grease lightly.
2. Inspect tubes for rust, dive and slush with slushing mixture.
MOTOR TORPEDO BOAT SQUADRONS
U.S.S. PT __________ Date _____________________
Check-off list for .60 caliber machine gun prior to firing
Check-off list to be completed before each firing.
Each part listed to be cleaned, oiled, and inspected to be sure that it is free of burrs or other damage, and is in operating condition.
1. Extractor cam.
2. Switch (works freely, no lateral play, nut pinned in place).
3. Breech lock cam has slight lateral movement, no vertical or longitudinal movement, screw staked in place.
4. Side plate trigger (works smoothly; nut tight and pinned in place).
5. Belt-holding pawl (spring strong, underside clean).
6. Retracting slide (nuts and screws tight, works smoothly).
7. Interior surface of receiver.
8. Feed mechanism (works smoothly).
9. Rear barrel bearing.
10. Cover extractor cam.
11. Cover extractor spring.
12. Cover detent pawl.
13. Cover latch.
14. Bore and chamber (clean and dry).
15. Barrel bearing surface.
16. Barrel extension.
17. Breech lock (double bevel forward and on top, works freely).
18. Firing pin hole clean, use only soft brush.
19. T-Slot (do not use metal object to clean).
20. Belt feed lever cam.
21. Remainder of bolt.
22. Firing pin extension (should not touch face of sears when retracted).
23. Sear (notch in good condition).
24. Sear slide (works smoothly).
25. Sear spring in good condition. Set in straight.
26. Sear stop pin not bent (replace, don't straighten).
27. Sear and firing pin operation.
28. Extractor (sharp edge of lug rounded off).
29. Ejector works smoothly.
30. Ejector spring in good condition.
31. Ejector pin in place.
32. Head space adjusted by bolt method.
33. Oil buffer body.
34. Oil buffer body spring (lock in good condition).
35. Oil buffer tube lock spring and stud in good condition.
36. Oil buffer tube completely filled with oil (USE BUFFER OIL ONLY), no air bubbles. Filling screws, relief valve screw, packing gland plug, and oil buffer tube cap tight.
37. Breech lock depressors (cam surfaces smooth, slight vertical movement only, rivets in good condition).
38. Driving spring rod straight, spring in good condition.
39. Head space tested after gun is assembled.
40. Gun tested for smoothness of operation (by hand).
41. Back plate buffer and adjusting screw hand tight with combination tool.
42. Ammunition inspected for faulty rounds and proper loading in chest.
Points to be Observed During Firing .50 Cal.
It is to be understood that these points are to be observed as occasion arises or opportunity permits. Firing is not to be interrupted merely for the purpose of observing them.
1. Clean bore and chamber.
2. Oil working parts and cam surfaces.
3. Tighten back plate buffer adjusting screw.
4. With gun unloaded, pull trigger and inspect face of bolt to see if firing pin protrudes. (Inspect for broken firing pin.)
5. See that nuts on mount are tight.
Points to be Observed After Firing .50 Cal.
1. Unload gun.
2. Disassemble gun.
3. Clean bore and chamber.
4. Clean all parts.
5. Inspect all parts for breaks, fractures, burrs, wearing, and operation. Use check-off list so as not to overlook anything.
6. Inspect and fill oil buffer tube. If it shows signs of leakage, locate leak and remedy.
7. Reassemble and adjust gun for firing.
CASUALTY REPORT FOR ORDNANCE EQUIPMENT
Unit name or description (Mk. Mod.) ______________________
Part No. or description __________________________________
Nature of damage__________________________________________
Cause of failure__________________________________________
Spares on hand____________________________________________
Note: This report to be signed by commanding officer or executive officer of PT and turned in to gunnery officer.
20 mm. Upkeep
Weekly or as necessary from exposure and as soon after firing as possible.
- Disassemble entirely and clean.
- Oil double loading stop very lightly and reassemble.
- Inspect barrel springs carefully for signs of corrosion or fatigue failure.
- Examine face piece carefully.
- Examine hammer for cracks.
- Assemble breech bolt and check protrusion of striker, pin in firing position.
- Reassemble complete gun oiling lightly first. If necessary a little heavier oil than recommended may be used exceptin double loading stop.
- Barrel should not be oiled outside and only with light oil inside.
- Before assembling barrel in place examine chamber entrance for burrs, dents, etc. This must be a smooth cone.
- After reassembly check trigger, trigger mechanism parallelogram for movement and for open assembly.
- Check interlock rod for operation.
20 mm. Before Firing
- Cock gun.
- Put on safety.
- Trip interlock gear by hand.
- Be sure ammunition is properly greased.
- Put tension on magazine.
- Place magazine on gun locking in place.
Depth Charge Upkeep
- Clean flanges on pistol and booster extender.
- Take off cap, check inlet holes.
- Take off safety fork and work booster in and out.
- Put on safety fork and cap.
- Run depth setting from 0 through 300 to 30 feet and back.
- Regrease flanges on pistol and booster extender.
- Take off booster extender and take out booster can with safety fork on.
- Take out pistol being very careful that setting is on safe.
- Inspect detonator for dampness.
- Wipe off flanges on pistol, booster extender and case.
- Wipe out central tube and oil lightly.
- Inspect booster can for loosening of top and bulging. Insert booster and see that it moves freely.
- Insert booster extender (see that gasket is good) and set up evenly on flange studs.
- Take off fork and move booster extender spindle back and forth to see that it waves freely.
- Insert pistol (see that gasket is good) and set up evenly on studs.
- Take out pistols and boosters and test with test set as per BuOrd instructions for use test sets.
Routine Upkeep of F. S. Smoke Generator
Grease bearings of release rollers.
Remove and clean nozzles. Replace and check setting at two turns.
Weigh CO2 bottle.
Check slip joint for tightness.
Clean and test reducing valve and gauge.
Literally Decoded, Gentlemen, It say, 'Nuts To Us.'
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