276,894. Destree, J. Jan. 11, 1927, [Convention date]. Breech actions, sliding breech-block.-The movement of the gas piston, or the equivalent, of a gas-operated gun of the kind in which the operative stroke of the piston is effected directly by the gases, is restrained by the gases themselves acting directly on the piston in the reverse direction. As shown in Fig. 1, the barrel 1 has two large gas ports 2, 12 communicating with the ends of a cylinder 3 containing the piston 4 which opens the breech during its backward stroke. When the gun is fired, the gases first enter the front of the cylinder through the port 2 and then, as soon as the projectile has uncovered the port 12, enter the rear end of the cylinder and oppose the movement. An opening 13 or openings leading to the atmosphere may be provided in the cylinder to reduce the braking effect. In the automatic pistol shown in Figs. 2 and 3, the breech-slide 21 is looked by a vertically-sliding bolt 20, 20<a> adapted to be driven down by the gases passing through a port 18<a>. A second port 18<b> in front of the first leads to the other side of the bolt 20 so that the movement of the bolt is damped by a jet of gas driven in the opposite direction. Specification 274,031 is referred to.