An assembly of a breech (1), a breech block (2) and an ejector (3) wherein the breech (1) is connected to the breech block (2) with the use of a groove (10), arranged in the breech block (2), and a corresponding recess, arranged in the breech (1). An ejector (3) is arranged in the breech (1) that is longitudinally adjustable in a sliding way between the front and rear end position. The ejector (3) is biased by a spring (6) against the shooting direction. On the back of the ejector (3) a recess is arranged that a peg (7) that protrudes from the breech (1) reaches into. At the rear side of the ejector (3), a longitudinal pin (4) is arranged that fits into an opening (5) in the breech block (2) in the rear end position of the ejector (3). On the part of the ejector (3) that protrudes out of the breech (1), a stop surface (9) is arranged for bearing on the breech guide (11) that protrudes out of the breech (1) block.