one extremity of which engages a recess 32 provided on the trigger 7 while the opposite extremity of the rod 31 is connected to a transverse spine 33 that is rotatably inserted in the handle 3 as shown in fig2 in this manner the orientation of the rod 31 of the spring 30 with respect to the pin 7 39 varies with the displacement of the trigger 7 it follows that the direction of push of the spring 30 is oriented eccentrically with respect to pin 7 39 of the trigger 7 and varies with the angular displacement of the trigger 7 about the pin 7 39 so that the couple which results is always substantially constant the actuation of the trigger 7 is thus smoother and safer in that it is not necessary to increase the pulling action as the trigger 7 is displaced due to the disengagement of the hammer 10 at the time of firing a further feature of the present invention concerns the mounting of the rotating drum 17 on the body 2 of the weapon the drum 17 is rotatably mounted in a manner known per se on its supporting shaft 35 within which extends a spring loaded rod 36 that is subjected to the action of a pusher 36a and which serves to block.