Modellers reference 75mm pak mountain gun

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75 M/M

O"W

MOUNTAIN GUN

NATIONAL FORGE & ORDNANCE CO. IRVINE, WARREN COUNTY, PENNA., U. S. A.

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75 M/M MOUNTAIN GUN FIRING POSITION

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GUN

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75 M/M MOUNTAIN GUN TRAVELING POSITION ON WHEEIJS

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SPECIFICATIONS Diameter of Bore

2.952"...

Length of Rifling

M/M 62.29"...1592M/M 2r.l 52.90"...1344M/M

Number of Grooves

28

Width of Grooves

.

.1966"...4.739M/M

Depth of Grooves

.

.030".

Length of Barrel, Including Chamber Length of Barrel, in Calibers

75

.. .762M/M

Width of Lands

.1444...3.672M/M

Rifling

IJniform, Right-hand Twist, One Turn in

25

Calibers

Muzzle Velocity

1440 Feet per Second 438.9 Meters per Second

Volume of Powder Chamber

45 Cubic Inches . . .737.4 C.C.

Density of Loading (approx.)

.630

Travel of Projectile

52.9"

Weight of Projectile

14.5 lbs. . . .6.577

Weight of Charge (approx.)

15.3 oz. . . .433.7 Grams

Powder Pressure (approx.)

23,000 lbs. per Square Inch 1617

Maximum Range

...L344.M/M

Kc

KG per Square CM

10,690 Yards . . .9,775 Meters

Range of Elevating Mechanism

-5 Degrees. . . 50 Degrees

.

Traverse Right

15 Degrees

Traverse Left

15 Degrees

Weight of Cartridge Case

2lbs.....907KG

Length of Cartridge Case

8.75"...222.25M/M

Center Line of Barrel to Ground Line

40" .

Wheels

32" Diameter, 4tt Tire Steel Wheel, of

Wheels on

Maximum Length of Recoil

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Ground 48" . . . L2L9.2 M/M

.

-

.. 1016 M/M

Rubber Tire or 6" Center to Center

,

33.78,, . . .858

-20

Solid

Pneumatic Tires

M/M

7 5 rvrlM MoUNTAIN

GUN

SPE CIFICATIONS -

(co,,tinued

)

I

W.iUht of Gun in Firing

,I '

Barrel Breech Mechanism

One-piece Forging, with Screwed-on Breech

I

Cradle

With Tobin Bronze Slides to Support

I II

position

1825 lbs. . . . 827.8 KG

Gun

Semi-automatic, with Vertical Sliding Wedge Block Recoil_

ing parts of Gun

Spring-Recuperators

To Balance the Tipping Parts of Gun at

Al1

Times I

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Recoil

Brake

Hydro_pneumatic

with Hydro Counter _

Recoil Buffer

)

Carriage Upper Carriage f,ower

Welded Construction with Ball Bearings Welded Construction with Ball Bearings

I

sptit Trails

Length of Trails from Center of Wheels to Trail Spades: 94.5" ...2400ls,{/M

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Loads

Maximum Load. . . 255 lbs. . . . 115.7 KG

Barrel Breech Cradle Upper Carriage

225 lbs. . . . 102.05 165 lbs. . . .74.84

KG

KG

255 tbs. . . . 115.20 KG

.-

255 lbs. . . . 115.70

KG

Lower Carriage

Wheels

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255 lbs. . . . 115.7

I

KG for 2 with pneumatic

I7S lbs. . . .79.37 Tires

KG for

2

with Solid Rubber

Tires

Trails

Equilibrators Upper Shield Lower Shield Total Weight

315 lbs. . . . 142.88

KG for

60 lbs. . . . 27.2 for

2

170 lbs. . .

2

.77.t KG

60 lbs. . .

.

1825 lbs.

with pneumatic Tires . . . g27.8 KG

f'SOS

tns.

27.2 KG

with Solid Rubber Tires . . . g64.1 KG

7 5 M/M M O U N T A I N

GUN

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METHOD OF ASSEMBI,ING GUN FROM PACK ANIMAIJS 1-Unpack the lower carriage, wheels, and trails.

2

(Fig. -Unfold trails

to traii hinge.

Fig.

3-Place wheels on axle

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sleeve

2

with counterbored part of hub next to trail (Fig. 2).

.7 5 MM

MOUNTAIN

GUN

Fig.

3

4-secure in place by winged hub nut. Drive nut tight with lead hammer (Fig. 3).

5-Lay

wheels with trails attached on thb ground about four feet apart, hub cap down

(Fig. a).

6-Set lower

carriage arm in axle yoke with detent pin in its recess.

7 5 M/M MOUNTAIN

GUN

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7-Swing carriage about detent pin to vertical position and insert king pin (Fig. ,

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8-Tip

lower carriage, wheel, and trails about wheel as a fulcrum until lower carriage is horizontal.

9

up remain-

-Stand ing wheel with trail

attached and slip axle yoke over end

of lower

carriage (Fig. 6), insert king

pin.

Fig.6

Pose

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5

M/M

MOUNTAIN

GUN

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Fig.

7

11-Close trails to traveling position and lock with detents (Fig. 7). l2-Clean any dirt or foreign matter from polished fitting surfaces of both upper and lower carriages.

13-Set the upper carriage into the lower carriage (Fig. 8), with carriage arms toward trail spades.

Fig.8

75

M/M MOUNTAIN

GUN

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t 14-Twist the upper carriage about vertical center line until the lugs on upper carriage pintle sleeve enter their recesses in lower carriage. The carriage will then drop into place and the foot treadle locking device on the lower carriage will lock the upper carriage to the lower carriage. CAUTION must be exercised to see that the upper carriage is down firmly against the shoulder on top of the lower carriage. When the carriages are properly set together the foot treadle will be up to the position it occupied before upper carriage was set in place and the lower surface of the traversing gear housing will be flush with the mating ring on the lower carriage. l5-Raise the trunnion caps on the upper carriage by pressing in on the trunnion cao locking detents.

16-Add the

recoil

meihanism (Fig. 9),

including the cradle and trunnion bearings by placing the trunnion bearings

into the bearing

pedestals.

17-Engage elevating gear sector with pinion (Fig. 10).

Fig.

10

18-Close trunnion caps making certain trunnion cap detents are locked.

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75

M/M

MOUNTAIN

GUN

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19-Elevate the cradle and recoil as-

sembly to its limit.

I I I I I Fig.

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11

20-Set the counterpoise trunnions in the sockets provided for them on the upper carriage and tip them back until holes in their upper end lines up with the holes in cradle arms (Fig. 11).

I 21-Insert locking

I

pins (Fig. 12).

I

Fig.

12

22-Depress the recoil mechanism to horizontal. CAUTION: With the counterpoise in place do not open trunnion caps unless gun is at maximum elevation, which removes tension from counterpoise springs.

7 5 M/M MOUNTATN

GUN.

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Fig.

13

23-Place barrel across trails (Fig. 13).

24-Open breech, clean and oil threads on barrel and breech. Remove all oil from shoulders on barrel and breech housing.

Fig.

14

25-Screw breech housing onto barrel by means of the interrupted tfrleaas (Fig. 1a.)

Pose 12 .

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7 5 M/M

MOUN

TAIN

GUN

26-Hold barrel from turning and set breech housing securely on barrel by giving quick turn. '

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27-Pldce lifting bars through lifting eye on breech and through eye near muzzle.

28-Slide barrel and breech assembly onto the lugs provided for it on top of recoil

cylinder (Fie.

15).

The breech housing

locking lug at extreme rear end of re-

coil cylinder must enter mating recess in breech housing.

Fig.

15

29-Insert barrel locking pin (Fig. 16)

through barrel and recoil cylinder to retain barrel in place.

Fig.

16

breech must always be opened when assembling or removing breech housing from the barrel (Fig. 13). Opening the breech draws the extractors away from their recesses in the rear face of the barrel permitting the breech housing to

30-CAUTION: The be unscrewed.

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GUN.

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31-The lower

shield (Fig. 17) is added by simply dropping the tapered bracket ends into sockets on lower carriage. The brackets may be driven

into the sockets with the lead

ham-

mer.

Fig.

17

Fig.

18

32-With the upper shield in its folded position (Fig. 18), remove the two chained. pins which hold the lower and middle shield brackets together. Lift both brackets away from the shield and replace pin through hole in end of middle bracket and through lower hole in lower "Y" brackets thus forming a triangular shaped brace. The shield is then opened out flat and brought to the gun.

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75

M/Nr

MOUNTAIN

GUN

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33-The barrel

and

recoil mechanism is Fig. 19 inserted through the large opening in the center of shield (Fig. 19), the lower bracket is set on the lower shield and slid back until the "C" opening in triangular brace fits over the flat-sided pin on upper carriage. The shield is then tipped back and the top "Y" brace is placed. over the nut and pin at the top of carriage arms.

The nut is

by a

secured

wrench (Fig.

20).

Fig.

75

M/M

20

MOUNTAIN

GUN.

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34-The center slide is then inserted in the slides provided for it on the shield (Fig.21), and the hold down tape on main shield is attached to hook on slide.

Fig.

21

Fig.22

35-Place sight mount, with sight attached, on left trunnion extension. It will be held in place by the rotating lock (Fig. 22), and two clamp screws. These screws must be tightened if sight remains on gun when firing.

36-Remove sight and sight mount when transporting gun on wheels.

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MOUNTAIN

GUN

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37-To dismount the gun reverse the order of assembly.

To remove upper carriage press foot treadle (Fig. 23).

Fig.

23

Fig.24

GENERAIJ INSTRUCTIONS 38-Two locks are provided to lock gun

during

transport. One under the cradle locks the cradle to the upper carriage. The other at the rear of the lower carriage locks the upper and lower carriages together. These locks must be released before elevating or traversing the gun.

39-Leather boots are provided for each end of barrel, for the threaded end of breech housing,(Fig. 24), and for the lower end of the pintle sleeve (Fig. 25).

Fig.

75

25

M/IvI MOUNTAIN

GUN.

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40-The sight

and

sight mount are to be assembled and packed in wooden boxes provided for

their protection (Fig. 26).

Fig.

41-A tool box

26

is

provided which con-

tains all the necessary tools for field maintenance and repair. An oil PumP'

with

necessary fit-

tings, also gauge and metal hose for nitrogen tank connection

are provided (Fig. 27.)

Ftg.27

42-A small nitrogen tank is provided with each gun to

replenish nitrogen

in recoil

system,

Page

18

.7 5 M/M MOUNTAIN

GUN

pressure in the recoil system must be maintained at.400 to 450 pounds' This should always be checked, before firing gun if gun has been inactive for several days' Remove The nitrogen filler plug will be found in the muzzle end of the left recoil cylinder' con(Fig. which 28)' assembly adapter filling nitrogen plug and screw in the

45-The nitrogen

the filler in, sists of the filler connectioll, gauge, and shut-off valve. when the adapter is screwed check the trip will extension adapter The pressufe. the valve should. be closed to test valve in recoil system and the gauge will rFcord pressure in cylinder.

Fig. 30

46-If the gauge reading is less than 400 pounds the pressure

must be increased by

attaching the nitrogen tank to the gun by means of the flexible metal hose and the filling adapter (Fig. 30). Open valve on tank and meter the proper amount of nitrogen into system by opening the adapter valve a very small amount. Shut off valve occasionally to check gauge reading. When gauge reading is 450 pounds shut tank valve and plug. adapter valve. Disconnect metal hose and remove adapter assembly. Replace filler

_lf for any reason it is desired to drain nitrogen from recoil system, the adapter should put in place as when checking pressure. The valve can then be opened to drain system: be 47

48-After draining the nitrogen, the oil may be drained by removing oil filler plug and' holding down check valve with a small steel rod. The oil gauge body may also be removed to drain oil if necessary. This should not be attempted without first removing nitrogen from the sYstem.

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75

M/M

MOUNTAIN

GUN

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METHOD OF PACKING 75 M/M MOUNTAIN GUN ON

PACK ANIMALS

UPPER CARRIAGE ON PACK

75

M/M

MOUNTAIN

GUN

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WHEELS AND TOOL BOX ON PACK

UPPER SHIELD AND HINGED TRAILS ON PACK

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GUN

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LOWER CARRIAGE, LOWER SHIELD AND SHIELD SLIDE ON PACK

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GUN.

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BARREL ON PACK

BREECH, RECUPERATORS AND SIGHTING EQUIPMENT ON PACK

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SIGHTING To veilfy parallelisrn of line of siEht and axis of bore

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BOR,E

Fig. 31

When

it

is desired to check the parallel-

ism of the line of sight of the panoramic telescope and the bore of the gun the following method should be followed: A target should be made to dimensions shown in Fig. 31. The background of target should be painted white and the aiming points black.

The carriage is placed with the wheels and trails resting upon solid supports of wood, stone or concrete, the surfaces of which have been carefully leveled so as to bring the axle axis horizontal. The barrel is carefully leveled and a bore sight iq placed in the bore. The target, Fig. 31, is set in line with the barrel at a distance of 150 to 200 feet from the muzzle and in

7 5 M/M MOUNTAIN

a vertical position perpend,icular to the line of sight and at such a height that the horizontal prolongation of the center line of bore intersects point "X" on the target.

The verticality of the target may be assured by dropping a plumb line from point "A" which should coincide with line "AB".

The gun is carefully bore sighted on target at point

"X".

The panoramic tele-

to the sight mount. The mount with telescope attached is placed on the left trunnion extension and held in place by the rotating lock. The sight mount is carefully cross-leveled by use of the knurled knob until the level bubble is in the center of vial. The elevating scope is attached

GUN

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Fig. 32

at "O" and also the elevating micrometer dial, which is the lower dial toward rear of mount. The angle of sight index, at top center of sight mount, should be set opposite "3" and its operating micrometer dial should be set at "O". With the mount so set the sight level bubble should be central with its vial.

If the level bubble is not central after making the above setting, either or both micrometer dials must be turned until the bubble is central with the level vial and the indexes as near as possible to "3" and "O". The index scales may be moved for adjustment by unscrewing their retaining screws and setting them opposite their corresponding indexes. After leveling the mount, and registering the index index should be set

Pcrge 26

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pointers with their corresponding scale setting, the three screws in the end of the micrometer dials are loosened and the dials turned until "O" on the dial scale is opposite the coresponding index on the sight mount body.

The screws are then tightened to lock dial to its worm shaft. When properly adjusted the "O" on both micrometer dials, and the "O" on the elevating scale should be opposite their index arrows and the "3" on the angle of sight scale should be opposite its index arrow with both level bubbles in the center of level vials.

With the sight mount level bubbles set central with their vials, set all dials and indexes on the panoramic telescope at "O". If the sight is properly set the line of sight through the telescope will pierce

7 5 M/M MOUNTATN

GUN

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the target at the point "Y". If the line of sight through the telescope does not terminate at point "Y" the telescope must

circular scale when making adjustments.

If the line of sight of the telescope is correct horizontally, but the cross hairs are above or below the aiming point "Y", the telescope should be so adjusted by use of the rotating head micrometer dial, which is the vertical dial at top of telescope, until the line of sight through telescope pierces point "Y". The three screws on top of the micrometer dial may be loosened and the dial set with its "O" opposite its mating indicator. Tighten screws and check line of sight to verify setting. The scale on the peep sight arm shows elevation in hundreds of mils. The "O" on this scale and the "O" on the dial should be set opposite, their mating indexes with the line of sight through telescope piercing point "Y" on target.

be adjusted.

If the line of sight is at the correct height but off to either side of the vertical

line through "Y", the correction should be made in the telescope. Set the cross hairs of the telescope on the target by rotating the lower micrometer dial. Loosen the three screws in the dial retaining disc and set dial

"O" to coincide with its indi-

cator on the sight body. If necessary the index plate, below the lower circular index, may also be adjusted by loosening the fwo index retaining screws. It should be noted that the upper horizontal micrometer dial should also be set at "O" and the index opposite "O" on the upper

Fig. 33

75

M/IvI

NIOUNTAIN

GUN

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FIRING MECHANISM ,-[]

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Drawing O.A.-110 . . . Firing Mechanism

of The firing mechanism (O.A.-110) is -\ the continuous pull type-located in an axial opening in the breech block. To disassemble the firing mechanism withdraw lanyard pin from trigger shaft and remove lanyard. With a screw driver press trigger shaft retaining detent, (O.A.-108-3 Drawing O.A.-115), out of engagement with trigger shaft and withdraw shaft. The firing mechanism housing (O.A.-107-1) is retained in its opening in the breech block by three lugs.

Turn the case 60 degrees either side of assembled position and it may be withdrawn from the breech block. Pry the trigger yoke O.A.-107-4, out of the firing mechanism housing with a screw driver.

Insert trigger shaft to engage sear O.A.107-6. Press the front end of sear out of

7 5 M/M MOUNTAIN

engagement with striker, O.A.-107-3, insert a screw driver at the rear of the sleeve O.A.-107-5 and pry the sleeve and striker forward until they can be grasped by the fingers and pulled from the case. Remove trigger shaft, and withdraw sear and sear spring.

To remove the firing spring, (O.A.108-6) from striker, hold front end of striker in one hand and press the rear of sleeve against any convenient object to compress firing spring. Press rear end of striker down to unhook it from sleeve and allow sleeve and spring to recede from striker. Remove the firing pin cotter and unscrew firing pin.

To assemble mechanism proceed in reverse order.

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MOUNTAIN

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BREECH MECHANISM The breech mechanism, (O.A.-115)' is of the vertical sliding wedge type, semiautomatic.

To open the breech pull the operating handle, (O.A.-112-1), on right side of breech housing to the rear until the extractors, (O.A.-113-4 and 5) lock the breech block open (down), the handle should then be returned to its original position and locked by the handle latch, (O.A.-114-5). When a round of ammunition is inserted the cartridge case head trips the extractors, allowing the breech block to return to its closed position under action of breech closing spring, (O.A'1

14-6).

To remove breech block from the breech

housing remove the breech closing spring

cap O.A.-114-7 and unscrew spring adjusting nut to relieve spring tension. Withdraw operating crank pin O.A.-111-2 and closing spring with attached parts. Remove lanyard pin O.A.-108-1 and withdraw lanyard. Pull cotter pin from end of locking plate key O.A.-112-5 and drive out key, slide locking plate O.A.-1L2-4 to the rear and remove it from bottom of breech housing (O.A.-105). Rotate handle to rear to unlock it from its latch. Move operating crank O.A.-111-1 to rear to remove it from its bearings. A slight rotation of handle and movement to the rear

75

M/ru MoUNTAIN

of the crank will allow the rollers on inner

crank arm to be removed from the "T" slot in bottom of the breech block. Remove the crank, and the block may then be pushed out of the breech housing from the top. The extractors can then be removed from their slots.

The firing mechanism may be withdrawn either before or after removing the block from breech housing. Method of removing firing mechanism from block is described under "Firing Mechanism".

The operating handle latch may be disrnounted from the side of breech housing by removing the cotter pin at the lower end of key O.A.-114-2 and driving out the key. Drive the latch assembly to the rear to release it from its dovetail. The plunger O.A.-114-5 and spring O.A.-114-3 are retained by the headed pin O.A.-114-4 which fits into the flat recess on the side of the plunger. Press the top of plunger against any convenient object to compress the spring and with a small screw driver or pin against the outer end of the retaining pin, it may be pushed out of the housing. The spring and plunger may then be removed, by gradually releasing the pressure on the spring. They can then be removed from the housing.

To assemble proceed in reverse order'

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GUN

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COUNTERPOISE To disassemble counterpoise assembly (O.A.-149-f), place it in a lathe between jaw chuck and tail stock centers and guided by the two steady rests as shown on O.A.-250.

Steady rest No. 1 is lightly clamped to the outer sleeve of counterpoise and se, curely clamped to lathe bed. The steady rest No. 2 is lightly clamped to inner sleeve of counterpoise and secured to the lathe bed loosely enough to slide freely on the bed as is the tail stock.

The counterpoise spring with the counterpoise extended as shown is under a pres-

sure

of about 350 lbs. and therefore to

7 5 IvIlM VIOUNTAIN

prevent injury to the personnel, caution must be exercised when assembling and disassembling this unit. IJnscrew the counterpoise locking nut and allow inner streeve, steady rest No. 2 and the tail stock to slide to the right, using the tail stock traversing crank to control the operation.

As the inner sleeve is withdrawn from the outer sleeve, the spring will become exposed and should be held from deflecting to either side by hand. At the point where the spring may tend to deflect its load has, of course, been greatly reduced.

To assemble the counterpoise proceed in reverse order.

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Pose34 ..7 5 M/M MOUNTAIN

GUN

ELEVATING MECHANISM The elevating mechanism is located on the left side of gun, secured to upper carriage by four cap screws. The eccentric housing which supports the elevating pinion is clamped at its inner end by four cap screws. By removing these eight cap screws the assembly may be removed from the carriage.

The assembly is shown on O.A.-143 and consists of a hand wheel, with overrurining clutch, a pair of bevel reduction gears, a self-locking' worm and worm gear and elevating pinion, housed in an aluminum case and equipped with ball bearings. The hand wheel may be locked to the shaft by pressing in on the locking jaw at the hub center.

To adjust the bevel gears, remove the oil filler plug at top of housing. IJnscrew the locking screws which lock sleeve O.A.-140-1 and retainer O.A.-139-3 in place. If only a slight adjustment is necessary it may be made by retainer O.A.139-3. If the back edges of the teeth are not flush as observed by looking through the oil filler hole, then the sleeve O.A.140-1 must be turned until they are, and at the same time maintaining the proper backlash, which should be just enough to allow bevel gears to turn freely without any perceptible looseness.

The worm wheel may be adjusted to the worm by rotating the eccentric sleeve O.A.-141-1 and locking it in place with

lock nut O.A.-141-3.

If it is desired to remove the parts from the housing, the following method should be employed. IJnscrew sleeve O.A.-140-l from the casing which will draw the worm (O.A.-139-5), bearings and bevel pinion

7 5 M/M

MOUNTAIN

(O.A.-139-2) to the rear far enough to be lifted out of housing by hand. The hand wheel with its shaft, bevel gear O.A.139-1, and bearings may be removed as a unit by removing the locking screw and unscrewing retainer (O.A.-139-3) which will draw the assembly out of the housing.

The worm wheel, eccentric sleeve, elevating shaft, with pinion, and bearings may be removed as a unit from the housing, by removing cover, 0.4.-140-6 and unscrewing the sleeve locking nut, O.A.141-3 and loosening the two lower clamp screws in the eccentric sleeve clamp, O.A.-

142. When removing the cover, O.A.at hand to catch the oil contained in the housing. These parts run in a bath of oil and when as140-6, a pail should be

sembling, the oil should be replaced. The worm wheel may be pulled from the shaft after removing nut, O.A.-140-3. The bearing adjacent to the worm wheel is retained by ring, O.A.-141-2. The shaft and pinion

with the two pinion bearings may be shoved out of the eccentric sleeve from the worm gear end.

To assemble the mechanism reverse the procedure outlined above; adjust the worm wheel to the worm and adjust the bevel gears as previously described. Lock the parts in place and filI housing with light gear oil to the height of the bottom of the hand wheel shaft. This lubricates all gears and bearings in the case. The two large bearings on either side of elevating pinion are packed with lubricant and require no

oiling.

One turn

of hand wheel elevates gun

1.33 degrees.

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TRAVERSING MECHANISM The traversing mechanism, (O.A.-148),

is secured to the rear face of the upper carriage gear housing by ten cap screws and two dowel pins. It consists of a worm mounted on self-lubricated ball bearings, inclosed in an aluminum housing. A hand wheel at the outer end is provided with an overrunning clutch and a locking mechanism to lock the hand wheel to the shaft if so desired. The worm meshes with a sector on the pintle sleeve which in turn is keyed to the lower carriage. One turn of the hand wheel traverses gun ll( degrees. Any axial looseness that may develop may be taken up by means of the adjusting sleeve, O.A.-147-2 and the locking nut O.A.-147-3.

To disassemble, remove the assembly from the upper carriage. Remove the four screws in hand wheel hub and the hub cap, jaw and spring. Drive out the

7 5 M/M MOUNTATN

tapered pin and remove hand wheel assembled to its hub. IJnscrew adjusting sleeve, O.A.-147-2 and lock nut O.A.-

147-3. The shaft with the two bearings the housing from the hand wheel end. The bearing at the hand wheel end of housing may be removed by unscrewing the ring O.A.-L+7-4 and pushing the bearing out from the opposite end of the housing.

at the worm may be driven out of

To assemble proceed in reverse order.

To adjust the worm to the worm wheel

a laminated gasket is provided between the gear case and the traversing gear housing. As wear occurs any backlash between

the worm and worm wheel may be removed by peeling off a lamination from the gasket, and replacing the traversing gear. If backlash still occurs after tightening cap screws an additional lamination may have to be removed.

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TRAVERSING MECHANISM The traversing mechanism, (O.A.-148),

is secured to the rear face of the upper carriage gear housing by ten cap screws and two dowel pins. It consists of a worm mounted on self-lubricated ball bearings, inclosed in an aluminum housing. A hand wheel at the outer end is provided with an overrunning clutch and a locking mech-

anism to lock the hand wheel to the shaft

if so desired. The worm meshes with a sector on the pintle sleeve which in turn is keyed to the lower carriage. One turn of the hand wheel traverses gun ll( degrees. Any axial looseness that may develop may be taken up by means of the adjusting sleeve, O.A.-L47-2 and the locking nut O.A.-147-3.

To disassemble, remove the assembly from the upper carriage. Remove the four screws in hand wheel hub and the hub cap, jaw and spring. Drive out the

7 5 M/M MOUNTAIN

tapered pin and remove hand wheel assembled to its hub. IJnscrew adjusting sleeve, O.A.-L47-2 and lock nut O.A.-

147-3, The shaft with the two bearings the housing from the hand wheel end. The bearing at the hand wheel end of housing may be removed by unscrewing the ring O.A.-L47-4 and pushing the bearing out from the opposite end of the housing.

at the worm may be driven out of

To assemble proceed in reverse order.

To adjust the worm to the worm wheel

a laminated gasket is provided between the gear case and the traversing gear housing. As wear occurs any backlash between

the worm and worm wheel may be

re-

moved by peeling off a lamination from the gasket, and replacing the traversing

gear. If backlash still occurs after tightening cap screws an additional lamination may have to be removed.

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RECOIL MECHANISM DESCRIPTION AND ADJUSTMENT The recoil mechanism, 0.A.-126 is of the stop O.A.-124-2. The oil then flows the hydro-pneumatic type consisting of through the communicating passage into three cylinders bored in a single forging. the recoil cylinder forcing the recoil piston The center cylinder contains the recoil back to the rear of its cylinder, and at the piston, piston rod and packing glands. same time compressing the air, which durAn adjustable respirator valve, (O.A.- ing recoil was drawn in through the res120-4), is located in the center cylinder pirator valve O.A.-120-4. The compresat the breech end. sion of this air cushions the return of the parts. Varying the amount of leakage The right hand cylinder contains the floating piston, oil gauge, (O.A.-122-5), past the valve by means of adjusting and recoil regulator, (O.A.-123-4). screw O.A.-120-5 alters the cushioning The left cylinder is an air reservoir and effect. is connected by a by-pass to the rear end The length of recoil may be increased of the floating piston cylinder. The forby increasing the length of stroke of recoil ward end of the left cylinder contains the valve. To increase stroke, loosen follower nitrogen filling valve, (O.A.-121-5).

O.A.-123-6 and unscrew regulator sleeve, In recoil the recoil cylinders (O.A.-116) O.A.-123-5 a fraction of a turn. One comslide to the rear with the barrel, being plete turn will open valve .083". The guided in grooves in the cradle. The piston normal stroke of this valve is .065. If this and rod are fastened to the front of the setting does not give 32" of recoil the gun re- opening must be increased by unscrewing cradle and do not move. As the the sleeve (O.A. 123-5) abott rl of a turn coils the oil at the front end of the main piston is forced through the passage leadand again checking length of recoil. The maximum length of recoil is 33.78" which ing into the regulator, opening the recoil valve O.A.-124-4 against spring O.A.-123-2 is controlled by the sleeve O.A.-119-2 and spring O.A.-119-1. The sleeve slides over until end of valve strikes lip on end of (O.A.-123-4). the communicating passage between recoil control mechanism housing piston cylinder and regulator, cutting off the flow The oil forces the floating along its pressure of oil. Any additional load is absorbed cylinder, against nitrogen of 450 pounds per square inch. The recoilinC by the buffer spring O.A.-119-1. parts are thus brought to rest by the The counter recoil valve stroke may be throttling of the oi1 through the recoil adjusted by loosening the follower (O.A.124-3) and screwing the stop (O.A.-L24-2) valve, the resistance offered to the floatpiston in ing by means of a screw driver, to shorten by the nitrogen and friction of parts. valve stroke. To lengthen valve stroke the gun is returned The to battery by the unscrew the stop. Hold stop in place and nitrogen aid of the compressed behind the tighten follower with socket wrench. One floating piston, which pushes the piston. turn of stop alters valve stroke .055". back and forces the oil into the regulator The normal valve stroke is .220 inch.

The tool box contains a set of socket and as the balanced recoil valve is closed pushes its due to action of spring, the oil wrenches with which to make these adthe counter recoil valve O.A.-124-1 open justments.

The recoil system holds 85 cubic inches until the end of its stem strikes bottom in

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of oil (about 114 qtatts)' However'

174

quarts is the maximum amount to be used when refilling.

The cylindrical projection of the front floating piston nut, O'A'-122-2 acts gun as a valve to retard the movement of into battery when oil level in system is low, thus giving warning to the gunners in case the oil gauge position has not been

end. of

minor adjustments should be attempted in the field. If for any reason the system does not function properly it should be disassembled in the ordnance repair shop' To remove the main Piston rod and piston assembly from the center cylinder' lhe respirator O.A.-120-1 should be removed from the breach end of cylinder' also the copper gasket O'A'-120-7' The

noticed.

Recoil Piston to Recoil Cylinder Drawing O.A.-198-1 . . . Method of Applying

For satisfactory operation enough oil should be maintained in the system to keep the oil gauge stem O'A'-122-5 flush Methods of -ittr tt. top of gauge body' under covered are oil and nitrogen filling general instructions.

To Disassemble Recoil SYsfernr First remove the nitrogen filler plug O.A.-121-4 and insert the nitrogen filler adapter, with gauge and shut off valve attached which will be found in tool box' The small projection on end of adapter will trip check valve O'A'-121-5 allowing nitrogen to flow into the atmosphere and ,educe the pressure in the system to that of the atmosPhere.

CAUTION: No Part of the recoil sYs: tem should be taken apart without first removing the nitrogen. No repairs except

7 5 M/M MOUNTA

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piston rod with piston assernbly may then te pushed out from the rrruzzle end' The stuffing box at m'tzzle end maY then be unscrewed and removed' IJnscrew the regulator housing O'A'123-4 with its parts in place' Remove the cap O.A.-119-7 in the breech end of the floating piston cylinder' The floating piston may then be pushed out of its cylinder

from the

rrruzzle end

with a brass

or

bronze rod.

The oil gauge housing O'A'-122-4 with its contained parts may be unscrewed as a unit.

The nitrogen filling valve may be removed by unscrewing the front cap O'A'l2l-2 from the left recoil cylinder' No description is necessary for the completed disassembly of these units, as this is self-evident from their construction'

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Drawing O.A.-199-1 . . . Method of Applying piston Rod Stuffing Box Packing to Recoii Cylinder

from any foreign matter, and. that cylinder walls are lubricated with a light film of recoil oil.

The recoil piston assembly is first inserted in the center cylinder bore from the breech end with the aid of the sleeve O.A.-198-2 which is first placed in the

the sleeve after forcing packings against the shoulder in cylinder and follow up with bushing housing O.A.-119-5. This should not be set up too tightly.

The respirator assembly should next be added to the breech end of center cylinder.

This should be screwed up tightly against

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Drawing O.A.-199-2 . . . Sleeve

breech end counterbore of the center cylinder as shown in O.A.-198-1. The pack_ ings are lubricated and the piston pushed into the cylinder until about 4 inches of the rod extends through the front end of cylinder. The stuffing box, packing, gland and nut are then applied to the front end

of the cylinder as shown on

O.A._199_1.

The packing should be oiled before apply_ ing and both packings with their followers should be pushed through the sleeve O.A._ 199-4 at the same time to prevent air pockets between the packings. Remove

7 5 M/M MOUNTATN

Drawing O.A.-199-3 . . . Sleeve

the copper gasket with aid of the socket wrench and a lead hammer.

Next apply the floating piston to the right cylinder aided by the sleeve O.A._ 198-4 which is inserted in the counterbore at the breech end as shown on O.A.-19g_3.

The piston glands and packing must be oiled before assembling. push the piston toward the front of the cylind.er with a copper or brass rod until the forward. end of the conical nut is just visible through the oil gauge opening. Screw in the regu_ lator against the copper gasket and also

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(O.A.-119-7) in breech end against its copper gasket. Set both up tightly with the socket wrench and lead hammer. Screw in the oil gauge body and its contained parts, the oil filler assembly, and the front cap containing the nitrogen filling valve. Make certain these are securely tightened against their gaskets.

The system is then ready to charge with

oil and nitrogen as previously described.

The gun is then read.y to be fired. Any minor adjustments to vary the recoil or counter recoil may then be made as previously described.

IJse special recoil oil furnished with gun.

Additional oil may be obtained from the National Forge & Ordnance Company.

3

Drawing O.A.-f99-4 . . . Sleeve

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