A muzzle member is mounted on the forward end of a gun barrel in such a way that a radial play-free mounting is effected which is secured against rotation and oscillations which occur at firing due to the finishing tolerances of the machined parts of the muzzle member.This object is achieved by constructing the front end of the gun barrel frusto-conically in front of an external threaded portion and constructing the rear inner portion of the muzzle member frusto-conically. An external threaded portion is provided on the gun barrel and an inner threaded bore portion is provided on the muzzle member for mating meshing mounting. The respective frusto-conical portions of the gun barrel and muzzle member have a length l.sub.1 is larger than 1.5 d.sub.1 thereby making for a radial play-free joint. The muzzle member is constructed in the longitudinal region l.sub.1 of the inner frusto-conical portion in such a way that a firm screwed connection will cause an elastic expansion for receiving a safety locking mechanism in the form of at least four recesses disposed on the outer surface of the frusto-conical forward end of the gun barrel which, in coaction with a rod serve as a rotational locking means.