A hammer assembly of the automatic mechanism of a firearm, comprising a breech (4) that is pushed towards the barrel (3) by a return spring (6). On the breech (4) and/or in the breech case (3) a hammer carrier (10) is arranged in a sliding way that is pushed towards the breech by a striking spring (13). The hammer carrier (10) carries a hammer (11). The hammer (11) is arranged on the hammer carrier (10) movably between the front end position and the rear end position wherein between the front and rear end positions of the hammer (11), there is a play (F). The hammer (11) is pushed to the front end position by the hammer spring (12).