Patent GB-1446664-A (GB)
Title: Automatic shoulder arm
IPC: F41A19/02
Filed: 1974-05-21
Abstract: 1446664 Automatic small arm HECKLER & KOCH GmbH 21 May 1974 [24 May 1973] 22557/74 Heading F3C An automatic small arm has a receiver 1, Fig. 1, displaceably supporting a fully operative firing unit which comprises a barrel 3, a bolt mechanism 4, a bolt-closing spring arrangement, a cartridge-feeding mechanism 5, a gas-pressure operated loading-device, and a displaceable portion of a trigger mechanism, a stationary portion of the latter including a trigger 142 being fixed to the receiver 1 and operatively connected to the displaceable portion, and the receiver forming the stock of the small arm, wherein the firing unit as a whole is arranged to be displaced against the force or a counter-recoil spring in the longitudinal direction of the barrel 3 by the gas pressure produced upon the discharge of a round. The gas-pressure operated loading-device comprises gas cylinders 11, Fig. 2, the front ends of which are connected to the barrel 3 by a block 13 having radial channels 12 through which the bore of the barrel communicates and the rear ends of the gas cylinders 11 are connected to the barrel 3 by a cross-member 20. A trigger housing 7, Fig. 3, for the trigger mechanism is movable with the cross-member 20. The block 13, Fig. 2, has lateral shoulders 25 and the cross-member 20 has lateral shoulders 26. The rear end of the housing 7 has a slide 27 having lateral arms which engage grooves in rails 2 mounted in the receiver 1 and serving to guide and locate the firing unit. The front end of the bolt mechanism 4 has a tubular section with which the bolt mechanism is located on the rear end of the barrel 3, extending from the cross-member 20, and the rear end of the bolt mechanism engages the rails 2 with lateral webs 29. Coil springs 42 are arranged on the gas cylinders 11 and act as counter-recoil springs. A buffer arrangement is provided, for the firing unit which travels rearwardly during a number of successive shots, and comprises compression springs 43 arranged on the gas cylinders 11 and which surround the springs 42. The firing unit, when in its position of rest, contacts a counter-recoil buffer which permits a limited forward movement of the firing unit. Bolts 33, Fig. 6, are slidably mounted in an abutment attached in the receiver 1, whereby in the position of rest of the firing unit the heads 34 of the bolts are in a contacting relationship, under the force of coil compression springs 36 surrounding them, with the front side of the cross-member 20 connecting the gas cylinders 11  and the barrel. The firing unit is retained in its position of rest by a catch 39 mounted in the receiver 1, the catch being connected to the trigger 142, Fig. 5, mounted in the receiver, by means of a draw bar 41, the unit being released when the trigger is actuated. The catch 39 is mounted in a flange 32 of the receiver and a shoulder engages behind the cross-member 20 connecting the gas cylinders 11 and the barrel 3.  The gas pressure operated loading device comprises a sleeve 17, Fig. 1, surrounding the rear end of the barrel and the front end of the bolt mechanism 4, the sleeve being connected to pistons 15 arranged in the gas cylinders 11 by means of piston-rods 16, being in engagement with the bolt mechanism by means of locking members and causing the bolt mechanism to travel forward and to lock, and in which the recoil springs 18 are arranged concentrically to the piston-rods 16 inside the gas cylinders 11. The cartridge feeding mechanism comprises a magazine 6 arranged parallel to the barrel 3 and the claw arrangements articulated to the bolt mechanism 4, said claw arrangement removing the catridges 96 from the magazine 6 and inserting them in the space between the bolt mechanism and the rear end of the barrel. The stationary portion of the trigger mechanism comprises the trigger 142 and a rail 61, mounted in the receiver 1, extending parallel to the path of the firing unit whose rear end is pivotally mounted about a bolt 62 which engages the trigger 142. A lever 81, Fig. 4, connects to the trigger and is provided with an adjustable guide. A sear 72, is mounted in the receiver 1 and can be swivelled by a catch 76 attached to the trigger 142. Stops for the trigger and/or the guides for lever 81 are formed by surfaces of a selective fire axle 82, the latter also having a stop surface which serves as a safety for the trigger.  Members effecting firing comprise a catch-link and an interrupter 6 which is pivotally mounted on the catch-link. In use the automatic small arm can be set so as to fire single fire, automatic fire with a relatively low rate or fire, a burst of fire, say three shots, and repeated bursts of fire.