A barrel is fixedly inserted in and protrudes from a grip and comprises a barrel chamber. A piston is provided on the outside of said barrel and rigid therewith. A breechblock comprises a cylinder surrounding said barrel and piston before said grip and defining with said barrel an annular chamber, which is sealed against said barrel. Said breechblock is movable along said barrel to and from a forward position. A counterrecoil spring urges said breechblock to said forward position. A piston is disposed in said annular chamber and rigid with said barrel and arranged to be disposed at the rear end of said annular chamber when said breechblock is in said forward position. Transverse bore means are formed in said barrel and communicate with the interior of said barrel adjacent to said barrel chamber. Longitudinal passage means are provided, which are laterally enclosed and connect said transverse bore means to said annular chamber.
