Methods and apparatus are disclosed for a locked machine gun that includes a casing, a barrel, a locking breech mechanism, an abutment and a quick change attachment. The locking breech mechanism has at least one locking body. The abutment holds the locking body or locking bodies of the locked breech mechanism. The quick-change attachment is used to facilitate the removal of the barrel and insertion and attachment of a new barrel. A first part of the abutment remains on the casing when the barrel is being changed, and a second part of the abutment is firmly connected to the barrel. The quick-change attachment is equipped to bring about a separation between the first part of the abutment remaining with the casing and the barrel with the second part. Also, the second part of the abutment has a curved section which controls the engagement of the breech mechanism in the abutment when the breech mechanism closes.