Abstract: A firearm is formed by a housing, in which an assembly of a carriage and a barrel with a muzzle stop, and a breech are displaceably supported, and wherein the breech is equipped with a return spring that is supported on the rear support surface of the housing, has a counter weight displaceably disposed in a longitudinal space located between the housing and the carriage, on the support surface of which counter weight the rear end of the return spring is supported, and which is seated in the front position thereof on a front stop surface of the carriage.