The invention relates to a firearm comprising a housing (1) with a rigid barrel (2) arranged therein, a magazine that can be mounted in the receptacle of the housing (1) and provided with cartridges (4), a closure (3) that can be moved with respect to the housing (1) in the longitudinal direction of the barrel (2) and that is used to guide cartridges (4) from the magazine into a cartridge holder (5) or for ejecting empty cartridge cases. The closure (3) is mounted completely inside the housing (1) over its entire movement path. A sear frame (6) is coupled to the closure (3) which is tensioned by means of a closing spring (7) in the direction of the front closed position of the closure (3). The invention also relates to a locking block (8) coupled to the closure (3) when the closure is in the front closed position. The locking block (8) can be tensioned by a locking spring (9) in the direction of said position, and the locking block (8) can be moved when triggering a shot through the closure (3) by compressing the locking spring (9) only for one part of the movement path of the closure (3) until the decoupling position is reached together with the closure (3).