The present invention relates to a gun (1) with a barrel (4) which proximally delimits a firing chamber (6), and a slide (8) translatable between a forward configuration in which it closes the firing chamber (6), and a rearward configuration in which it is distanced from the barrel (4) to open said chamber (6). The orientation of the firing chamber (6) in the forward configuration and in the rearward configuration is substantially parallel to the longitudinal axis (X). The gun (1) further comprises a locking device (10), which in the forward configuration acts so as to join the barrel (4) and the slide (8) and in the rearward configuration releases the slide (8) to enable its backward movement. The locking device (10) comprises at least one locking projection (12, 14) which, when the slide (8) and the barrel (4) are reciprocally released, guides the slide (8) in translation.