Firearms, particularly rifles, including an upper housing having a barrel, where the barrel and the upper housing are interconnected by means of a guide. In order to improve the connection, the guide includes corresponding prismatic guide surfaces that extend in parallel with the barrel shaft when the firearm is mounted and ready to fire, and the barrel is secured to the upper housing by a tensioning element that can rotate in the upper housing about an axis of rotation that extends normally with respect to the firearm center plane, and the tensioning element includes a tensioning portion and an actuating portion.