Abstract: In a firearm with a cylinder bolt mechanism, a locking chamber (27) is arranged in a space in the barrel between the rear end of the barrel and the rear end of the cartridge chamber for a bolt tip (28) on the bolt. Behind the locking chamber in the barrel is arranged a separate locking ring (23) between a stop (25) in the receiver and the rear end of the barrel. The locking ring is provided with lugs and grooves, and the bolt head is provided with corresponding claws which are able to pass through the grooves in the locking ring and to be rotated into the locked position ahead of the lugs in the ring. By introducing the bolt complete with the bolt head into the barrel and locking it securely in this position, it is possible to achieve greater accuracy because the bolt head acts as a stiffening connection between the barrel and the receiver, so that these components of the firearm are unable to move relative to each other as the result of oscillations in the barrel when the cartridge detonates.