We are going to find three families of semi-automatic pistols: , - With hammer: When we are going to pull the breech, we are going to arm the hammer at the same time. When the trigger is pressed, the hammer will be released to strike the striker, so that its head strikes the primer of the cartridge and allows the projectile to be fired. Ex: Beretta 92FS, Sig Sauer P226, Colt 1911... - Stryker (launched firing pin): Strykers do not have a hammer in their operating mechanism. When we are going to fire the breech, we will put the striker under tension (like a crossbow). Pulling the trigger will therefore release the striker which will strike the primer of the cartridge to allow firing. Ex: Glock, PFS9, Steyr C-A2... - Gas filled: Very little developed on handguns, it is a mechanism mainly used on assault rifles (AR-15, Ak -47). While a conventional semi-automatic handgun, the movement of the slide during firing is operated by recoil, the gas imprint works in the following way: the gases emitted during the combustion of the powder will follow the projectile inside the barrel. Just before the muzzle, a vent will redirect gases to the rear of the breech through the gas tube. The compression then decompression of the gases will activate the bolt for rearmament. The only handgun designed with this operating system is the Desert Eagle, which is the only semi-automatic firearm to fire .357 magnum, .44 magnum and .50 Action Express ammunition.