A self-loading firearm operating on the short-recoil principle which comprises a frame (1) having a handgrip (2) and adapted to receive a magazine. A breech block slide (3) is mounted for alternating longitudinal movement along the frame (1). A barrel (4) is provided which is able to move rearwards while positively locked with the slide member (3) by locking means (6 and 10). An actuating means (15 and 16) disengages the barrel (4) from the slide (3) after the high pressure period has passed. A cylinder (11) is located concentrically around the barrel (4) and communicates with the barrel bore (13) via passages (14). The action of propellant gases in the cylinder (11) retards the motion of the barrel (4) and slide (3) assembly allowing a lighter slide (3) to be used for a specific cartridge type.