Final Test Of Head Space Adjustment

Finally, test that the head space adjustment is correct as follows :—

Raise cover. Raise extractor.

With mechanism in its fully forward position, take hold of bolt handle and withdraw it to rear J inch; there should be no independent movement of bolt rearwards from base of barrel—i.e., barrel and bolt should move together to the rear.

If there is any such movement of bolt independent of barrel, head space adjustment is too loose.

To rectify, insert combination tool or point of bullet between right side of receiver and barrel notches, and screw up barrel one notch.

To test for too tight head space adjustment, work cocking mechanism backwards and forwards by means of bolt handle. If head space is too tight moving parts will not work smoothly ; the breech will bind as it is locked. The mechanism may not go fully home, when the trigger cannot be pulled to release striker.

To rectify too tight head space adjustment, insert combination tool or point of bullet between left side of receiver and barrel notches and unscrew barrel one notch.

Any such head space adjustment carried out must be tested.

PLATE 3 Internal Mechanism in Forward Position Boll (33) forward in firing position.

Extractor (33) gripping succccding round (in belt, not shown).

Cocking lever (35*1 in rearmost position.

Breech lock (52) forced up (by breech lock cam, not shown).

Breech lock pin projections (53) dear of lock frame projections (436),

Accelerator claws (44) tipped forward.

Barrel plunger and spring (46 and 47) released, having pushed home on barrel plunger stud on T-lug of barrel extension.

PLATE 3 Internal Mechanism in Forward Position Boll (33) forward in firing position.

Extractor (33) gripping succccding round (in belt, not shown).

Cocking lever (35*1 in rearmost position.

Breech lock (52) forced up (by breech lock cam, not shown).

Breech lock pin projections (53) dear of lock frame projections (436),

Accelerator claws (44) tipped forward.

Barrel plunger and spring (46 and 47) released, having pushed home on barrel plunger stud on T-lug of barrel extension.

backward movement of mechanism

BARREL

BARREL EXTENSION BOLT

ACCELERATOR MOVEMENTS

When a cartridge is fired, the force of the explosion drives the bolt (which is locked to the barrel by the breech lock in the barrei extension), barrel and barrel extension to the rear approximately f inch, when the breech lock clears the breech lock cam situated on the bottom plate of the receiver. The breech lock is now free to drop, and is assisted by the projections of the brcech lock pin striking the inclined forward surfaces of the lock frame projections. The bolt is thus free to continue to the rear. The rear of the barrel extension strikes the forward curved surfaces of the accelerator claws, tipping them backwards until the accelerator abuts the accelerator stop ; the accelerator locks in this position, locking at the same time the barrel plunger and spring which have meanwhile been compressed by the rearward motion of the barrel plunger stud. The barrel and barrel extension are thus locked in this position, and cannot continue further to the rear. During the tipping backwards of the accelerator claws above described, the accelerator tips are in

35 331 J2 35

35 331 J2 35

50 B3 « « « 1 47 43

PLATE ^ Internal Mechanism in Backward Position

(33a) Feed lever actuating stud cam groove,

(33) Extractor in position to guide grooved rim of cartridge into T cut of bolt.

Barrel extension (50) stopped from proceeding rearward by lock frame (43).

The inclined faces of the lock frame projections (43c) have struck the projections of the breech lock pin (53), forcing them down and unlocking bolt.

Accelerator claws (44) have been tipped backward and the barrel plunger(46) driven rearward, compressing barrel plunger spring (47).

Cocking lever (35) has been forced forward, thus cocking striker.

contact with the forward faces of the bottom extensions of the bolt. The accelerator acting as an increasing lever assists and accelerates the bolt to the rear. During the rearward movement of the bolt, the tip of the cocking lever located in its socket in the top plate of receiver is forced forward, thus withdrawing striker to rear, compressing striker pin spring and engaging bent with sear.

During the above rearward movements of the mechanism the driving spring is compressed. Any remaining rearward motion of the bolt which has not been overcome in compressing the driving spring is absorbed by the buffer recoil mcchanism.

EXTRACTOR

FEEDING OF SUCCEEDING ROUND

During the backward movement of the mechanism, the extractor withdraws the succeeding cartridge from the belt; as the extractor reaches its rearmost position it is forced down by the extractor cam in the cover, ready to position the succeeding round in the T cut of the bolt head.

Bottom Illustration : Shows bolt proceeding rear-toards, and the extractor withdrawing the succeeding round from the belt.

Top Illustration : Shows bolt in fully forward position. Cover raised to show the belt feed arm actuating study having been driven to the left when heated in cam groove of bolt. Thus the forward end of the belt feed arm has driven belt feed pawl to right3 thus positioning succeeding round against cartridge stops in feed way. The extractor is gripping succeeding round.

Bottom Illustration : Shows bolt proceeding rear-toards, and the extractor withdrawing the succeeding round from the belt.

feeding of belt feed lever belt stop pawl operations

During the backward movement of the mechanism, the feed lever actuating stud is located in the cam groove in the top of the bolt i thereby its forward end engaged in the belt feed slide is driven to the left. The belt feed pawl is permitted by its spring to ride up and over the next cartridge. The belt is prevented from being carried in the same direction by the belt stop pawl.

The backward movement of the mechanism has thus achieved the following :—

(a) The spent case of the fired round has been extracted from the chamber.

(b) The succeeding round has been extracted from the feed belt ready to be positioned into the T cut of the bolt head for feeding into the chamber.

(c) The striker has been cocked.

(d) The feed mechanism is in position ready to feed another round into the feedway.

(e) The recoiling springs have been compressed ready to reassert themselves to drive mechanism forward again.

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