A arms semi-automatic draws only one Munition with each action on its tail with relaxation and ensures only the operations necessary to recharging as long as the ammunition available allow it.

The energy created by the explosion of the ammunition is used to make function the mechanism of ejection of the case and loading of the following cartridge. If a ammunition is defective, the weapon is blocked and the shooting will begin again only after one operation aiming to eject it then to confine another of them.

A semi-automatic firearm automatically charges a cartridge in the room after a shooting, but a new pressure on the tail of relaxation is necessary so that it is fired. Thus, to draw ten blows with a semi-automatic firearm, it is necessary to press ten times of continuation on the tail of relaxation. On the contrary, with a entirely automatic Firearm, the shooting will continue as a long time as the tail of relaxation will be maintained inserted, until the exhaustion of the Munition S or the Incident of shooting.

There exist Pistolet S and Fusil S soldiers and of hunting semi-automatic. The large majority of the automatic weapons have an order which also allows the automatic semi shooting.

The semi-automatic weapons are sometimes divided into two categories according to whether their cylinder head S is or not closed before the action on the tail of relaxation. When the tail of relaxation of an open cylinder head weapon is pressed, the cylinder head advances, extracts a cartouche from the store, the place in the room and strikes it. With a system with closed cylinder head the cartridge is then already barrack room and the action on the tail of relaxation orders only the percussion. The system with closed cylinder head is generally more precise because causes less displacements of the center of gravity during the shooting. The system with open cylinder head is almost exclusively used in machine pistols because it is simpler and allows the gun and the room to cool more quickly.