In an automatic rifle which has been converted for non-military purposes to be semi-automatic by the removal of parts that allow its automatic function, additional suppressing elements are provided to ensure that the interruptor remains depressed until the bolt carrier fully passes the striker catch before the striker catch is engaged by the interruptor. This prevents premature connection of the striker catch and the interruptor, which could prevent sufficient striker spring pressure so that the next round can be fired. In one embodiment the trigger mechanism is fitted with an additional suppressing element (10) formed as a side push plate 7 on the bridge (6) of bolt carrier (5). In a second embodiment the interruptor is provided with a pin (8) protruding to the left, in a direction of fire, while the receiver side wall has a cavity (11), over which a thin metal sheet (9) with a beveled corner is placed such that between the lower edge of metal sheet (9) and the lower edge of cavity (11), as well as between rear edge of metal sheet (9) and rear edge of cavity (11) a gap (12) is provided to receive the pin. The additional suppressing element is particularly applicable to a Czech model SA vz.58 semi-automatic rifle which has been converted for non-military purposes.