Inside cylinder 1, attached to the barrel, is stationary rod 2 with piston 3. Piston 3 has lugs a which enter helical slot d on the inner surface of cylinder 1. Piston 3 can rotate with respect to rod 2 but cannot slide along it. Arranged at both ends of piston 3 are valves 4 and 5 with ports (grooves) b. The valves, held against rotation by keys e, can slide axially a certain distance. Upon recoil to the right, the piston turns on its rod, closing the ports of valve 4, held against the piston by the pressure of the fluid which is forced out through ports b behind the piston, and this brakes the recoil motion. Valve 5 is shifted away from the piston. Upon counterrecoil, the fluid flow is in the opposite direction. Braking begins only after the vacuum is filled, and is carried out by valve 5.
$3772$SHP,FD$