Patent ES-351867-A1 (ES)
Title: Improvements in or relating to breech mechanisms in automatic and semi-automatic guns
IPC: F41A3/26
Filed: 1968-03-22
Abstract: A breech mechanism for an automatic or semi-automatic gun comprises a breechblock 1 housed in a casing 7 which is non-rotatable and slidably mounted in a breechcase 8. The breechblock 1 is limitedly slidable in the casing 8 and means are provided between the same for producing a rotation of the breechblock 1 during the relative sliding such that lugs 3 on the breechblock 1 are brought into locking cooperation with lugs 4 on a sleeve 5 rigid with the gun barrel 6. The breechblock is further provided with a cup-shaped recess 2 at its forward end for the rear end of a cartridge to be fired. The outer surfaces of the lugs 3 and at least part of the outer surface of the casing 7 lie on the same cylindrical surface so that they co-operate with a complementary surface 18 in the breechcase, which surface forms a guide therefor. In the construction shown, the rotation producing means comprises a spindle 15 connected to a spring-loaded firing pin 16 at its mid-portion and to the casing 7 at its ends (Fig. 3, not shown). Adjacent each end the spindle carries a roller which works in a slot with a part helical surface in the breechblock 1 (Figs. 4, 6, not shown). At its forward end the slot has a straight portion such that the casing 7 continues on its forward motion with the firing pin 16 after the breechblock 1 is in its locked condition to fire a cartridge. In a modification (Fig. 2, not shown) the firing pin is more massive and is connected to the spindle through a lostmotion connection, that is, a slot in the firing pin, so that the cartridge can be fired earlier in the firing cycle and rebound of the casing sufficient to prematurely unlock the breechblock is prevented when the spindle engages the rear of the slot in the massive firing pin to stop the casing. In a further modification (Fig. 8, not shown) the casing is still connected to the firing pin by a spindle, but for rotation of the breechblock, the breechblock carries diametrically opposed trunnions carrying rollers, the rollers working in cam slots m the casing. The lugs 3 of the breechblock 1 are arranged in two annular rows with the rear locking faces of the lugs in each row lying in different helical paths (Fig. 6, not shown). The angle of the rear faces may cause the lugs 3 to be " reversible " or " non- reversible". Diametrically opposed channels 43, (44) are provided in the breechblock 1 for the passage of an ejector (35, Fig. 5, not shown) mounted in the breechcase 8 and a spring-loaded extractor 42. The breechblock 1 is urged to its cocked position by a gas-operated device 33 or by a resetting device (Fig. 2, not shown). The easing 7 is locked in its rearmost position on the breechblock 1 by an outwardly urged strip 51 (preferably urged by its own elasticity) which engages a shoulder of a projection 26 of the casing. The strip 51 is moved away from the shoulder by its engagement with a pushpiece 53 housed in the casing 7 when the pushpiece 53 in turn engages an inclined face 52 of the breechcase 8. The breech mechanism is held in its cocked position by a sear 32 and the mechanism is further provided with a return spring 36 and a damping device 11. The casing 7 is held against rotation in the breechcase by upper and lower longitudinally extending projections, the lower one of which operates the ejector on rearward movement of the casing 7.