Abstract: The present invention relates to a gun with a removable barrel, the barrel having a mounting rail connected to it and extending in the direction of the longitudinal barrel axis A, the barrel being connected to the system housing by means of a receptacle on the system housing, the receptacle being tubular at least partially in the direction of the longitudinal barrel axis A and the corresponding inner tube diameter dl being adapted to the outer circumference of the barrel, so that the barrel can be introduced into the receptacle in the direction of the longitudinal barrel axis A when the barrel is mounted on the system housing, and wherein the receptacle has a recess of the tube circumference which extends in the direction of the longitudinal barrel axis A, wherein the barrel is fixed axially with respect to the longitudinal barrel axis A by at least one connecting element and is fixed with respect to rotation at least in that the mounting rail extends in its longitudinal direction at least partially within th