Patent GB-977269-A (GB)
Title: Improvements in servo-trigger mechanisms for automatic firearms of the open breech type
IPC: F42C15/20
Filed: 1962-11-14
Abstract: 977,269. Automatic fire-arms. BREVETS AERO-MECHANIQUES S.A. Nov. 14, 1962 [Nov. 30, 1961], No. 43091/62. Heading F3C. Relates to a trigger mechanism for automatic fire-arms, e.g. heavy machine guns, of the open breech type, i.e. a fire-arm which immediately before firing, has the breechblock held in the open position against the action of a return spring, by a sear system which must be released to permit closing of the breechblock to cause introduction of a cartridge into the chamber and then ignition of the cartridge. According to the invention the trigger mechanism is so arranged that the energy to be brought into play for releasing the breechblock when the trigger of the sear system is operated, is supplied by the energy accumulated in the return spring when the breechblock is held in the open position, the energy being transmitted to the sear by means other than the surfaces of contact between breechblock and sear. In one embodiment a breechblock 1, Fig. 2, is urged to the closed position by a return spring 2 bearing against a member 4 slidable in the casing 3 and urged forwardly by a pulling spring 5. The spring 2 when it is compressed exerts a thrust of 50 kgs. and when expanded a thrust of 15 kgs. whilst the spring 5 exerts a maximum pull of 20 kgs. and a minimum pull of 18 kgs. A rod 6 on the member 4 has a projection 7 co-operating with an auxiliary sear 8 adapted to prevent rod 6 and member 4 from moving rearwardly. A main sear 11 is connected to the member 4 by means of a rod 9 and compression spring 10. When the mechanism is being set, breechblock 1 is moved rearwardly compressing return spring 2 against member 4 which is locked by the sear 8, and the main sear 11 engages and holds the breechblock in its rear position. When the firer disengages sear 8, member 4 moves rearwardly under the preponderant force of the spring 2 causing release of the main sear 11 as shown in Fig. 3 and forward movement of the breechblock to the closed position. Since now the pull of the spring 5 is now predominant the member 4 returns to its forward position and projection 7 engages sear 8. In another embodiment, a slidable member 4 Fig. 5 is located at a point in the return spring 2 such that when the spring 2 expands, a notch 7 in the member 4 is engaged by an auxiliary sear 8 before the breechblock 1 is engaged by the main sear 11. Thus when the sear 11 engages the breechblock 1, the front portion of the spring 2 between the member 4 and breechblock 1 is less compressed than the rear portion of the spring between the member 4 and a fixed abutment 12. On releasing the sear 8 from the projection 7, the member 4 is caused to move forwardly by the rear part of the spring 2 and a projection 13 thereon engages a pivoted finger 14 carried by the main sear 11 and disengages the sear 11 from the breechblock 1. In a further embodiment, Figs. 9-12 (not shown), the invention is applied to the automatic fire-arm described in Specification 963,119. The arrangement permits the firing of single shots as well as bursts and also ensures that when the last cartridge has been fired, the breechblock is engaged by the sears to hold it in the open position.