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together in such a manner that the link may swing on the pin as a pivot. The link pin also protrudes through a slot m the receiver to engage the operating handle. The recoil spring (55) is encased in the gas piston, its front end pushing forward on the piston while its rear end rests against the head of the recoil spring guide.

The sear (47) is pivoted in the sear carrier (51) by the sear pin which also holds the sear carrier to the trigger guard (52). The holes through which the sear pin passes in the trigger guard are slotted, allowing a slight horizontal movement of the sear carrier. When the sear engages in the notch of the moving slide, the counter recoil spring (53) acts as a buffer, allowing the sear carrier and sear to move instead of suddenly stopping the movement of the slide.

The ejector (54) is a flat spring which yields slightly when struck by the empty cartridge case so that the latter is gradually ejected.

Action _of 'the Mechanism, With the gjun in the ready-to-feed posi- tion and the change lever set for semi-automatic fire the cycle of operation when the trigger is pulled is as follows: The connector which is pivoted in the trigger moves the sear (47) out of engagement with the notch in the slide and is cammed forward allowing the sear to spring into position to engage the slide on its return. The recoil spring (55) which has been compressed during the recoil of the mech- anism, drives the piston (46) and slide (45), carrying the bolt (39), bolt lock (43), link (44) and hammer (49) forward. As they move forward the lower edge of the bolt strikes the upper edge of the top cartridge in the magazine and drives it forward into the chamber.

As the parts are nearing their forward position, the rear of the bolt lock (43) which curves downward, comes in contact with the rounded end of the bolt-supports (23) and the rear end of the bolt lock is started moving upward. As the slide moves further forward, the top end of the link, which is pivoted to the bolt lock, tends to move upwards as the lower end is swung forward with the slide, and the link forces the rear end of the bolt lock in front of the recoil shoulder in the receiver, thus positively locking the breech, as shown in the illus- tration. The motion of the bolt as the bolt lock swings upward, is gradually stopped so that the bplt is not stopped suddenly, but very gently as its forward horizontal motion is transformed into the ver- tical motion of the rear of the bolt lock.

The hammer strikes the firing pin and the cartridge is ignited. The forward shoulders of the slide then strike the heavy buttment of the gas-cylinder tube, and the motion is arrested.

After the bullet passes the gas port in the barrel near its muzzle, the expanding gases enter the gas cylinder and drive the piston and slide rearward. The rear of the bolt lock is brought down away from the recoil shoulder of the receiver, and is started back, gradually starting the bolt rearward with it, but by the time the bolt starts to move, the pressure of the gases has subsided, so that the empty car- tridge is no longer expanded against the walls of the chamber, but comes out freely. Extraction troubles are thus avoided. The bolt is both stopped and started gradually and is not damaged with hammer- like blows. The empty case is drawn from the chamber by the ex- tractor until its under edge strikes the ejector, when it is ejected to the right and forward ; this avoids interference with a man imme- diately to the gunner's right.

The recoiling parts are arrested when the slide strikes the buffer, and the sear once more engages in the sear notch, which holds the slide and bolt mechanism to the rear with the breech open.

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by an aluminum radiator with annular corrugations surrounding the barrel. The backward and forward motion of the barrel causes air to be driven into the holes in the radiator casing (cf. the Lewis gun, fig. 14) which also assists in the cooling. The locking of the bolt mechanism is positive and is done by two locking lugs on the bolt head which are rotated into locking recesses of the breech casing. Lugs are provided to guide the bolt head and bring it in contact with the cam cuts in the bolt body. The cartridges are fed from a semi- circular magazine holding 20 cartridges, when rim cartridges are used, and from a straight magazine when rimless cartridges are used. A regulator is provided, which adjusts the gun for safety, for auto- matic fire, or for semi-automatic fire.

The action of the mechanism is divided into two phases: the forward motion and the backward motion. The rifle is loaded by pulling the operating handle to the rear until the mechanism is arrested by the sear (57). A charged magazine is inserted into the magazine opening in the gun, the magazine being held in place by the magazine catch (58). When the trigger is pulled it causes the trigger bar (59) to rotate the hand sear (60) against the under side of the breech casing (61). This forces the sear lever (62) downward, de- pressing the sear and releasing it from the notch of the feed piece.

The bolt head (63), bolt body (64), firing pin, and feed piece move forward under the action of the mainspring, which is encased in the spring tube. The feed piece strikes the upper part of the head of the cartri Jge in the magazine and forces it forward out of the magazine. At this time the cartridge (*uide (65) is being held up by the roller working in the cartridge guide cam slot. The bullet is directed into the chamber, the magazine spring forcing the rear end of the car- tridge up into the path of the bolt head just as the cartridge is freed from the lips of the magazine.

The cartridge guide cam causes the cartridge guide to drop, thus letting the feed piece pass forward and release the barrel catch (66).

The bolt-head stop (67) keeps the bolt head and bolt body at their extended positions so that the locking lugs in the bolt head are ver- tical, thereby permitting their entrance into the locking recesses. The bolt-head stop then comes out of the breech casing, the bolt head is released and rotates so that the locking lugs engage in the locking recesses in the breech casing to lock the mechanism. The bolt body and firing pin continue to move forward, and the extractor grips the rim of the cartridge as the bolt head turns. The firing pin primes the cartridge just as the feed piece releases the barrel catch.

Backward motion : The recoil from the explosion combined with the action of the gases on the barrel nut (68) carry the breech mech- anism and casing in a locked position to the rear against the action of the recoil spring (69) and mainspring. The breech casing and barrel (70) being free to move, immediately start forward. The breech mechanism is held back, due to the sear engaging in the sear notch on the tail of the feed piece. As the barrel moves forward the empty cartridge case is drawn from the chamber by the extractor. As the barrel continues its forward motion the front end of the empty case clears the opening in the breech housing and it is thrown out through the ejection-opening by the pressure of the ejector upon its base. If the regulator is set for single fire the hand sear is immediately released by the trigger bar. This allows the sear to hold back the breech mechanism until the trigger is again pulled. If the regulator is set for automatic fire the hand sear is not released, but is held up

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FIG. ii. Chauchat Machine-rifle.

Chauchat Machine-rifle. The Chauchat machine-rifle, model of 1915 (fig. n^also known as Rifle C.S.R.G., was designed by a commission presided over by Col. Chauchat. It weighs about 19 Ib. and is about 45 in. long. It takes the 8-mm. Lebel car- tridge or, in the case of the guns taken over by the U.S. army, 1 the U.S. model of 1906 ammunition.

This rifle is recoil-operated ; the recoil being assisted by deflecting part of the gases as they escape. The cooling of the barrel is assisted

1 As already mentioned, the Browning gun was reserved until a large supply could be put into line at one time. Pending this, the American forces in France were equipped with the Chauchat of which some 34,000 were adapted to U.S. ammunition.

by the trigger mechanism. The rear cam surface on the bottom of the breech casing strikes and depresses the hand sear just as the barrel reaches its forward position. The hand sear forces the sear lever down, which in turn depresses the sear, releasing it from the sear notch of the feed piece. This allows the breech mechanism to go forward and repeat the cycle.

This rifle is provided with a forward grip (71) for use in marching fire. A bipod (72) is provided for prone or fixed position firing.

Hotchkiss Light Machine-Rifle (fig. 12) weighs 185 Ib., is air- cooled and gas-operated, magazine-fed, and provided with a bipod (73), a hand grip (74) and a shoulder stock. The general mechanism is the same as in the Hotchkiss machine-gun. The speed regulator and buffer mechanism is especially interesting.