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How do Semi-Automatic Pistols Funcion?

The semi-automatic pistol, also known as a self-loader, came about when many gunsmiths saw the potential for handgun applications that could be applied to Hiram Maxim's recoil-operated machinegun in 1883. Notable among the early models were designs by Borchardt, Paul Mauser and Georg Luger.

Although there are many famous semi-automatic pistols the most recognizable one is certainly the Colt Model 1911. This firearm is still manufactured today unchanged from it's original design and remains extremely popular. Sam Colt designed this pistol and it was adopted by the U.S. military in 1911 (hence the model designation).

The concept behind autoloading weapons is that part of the energy freed during the firing of a bullet is redirected to perform the work of ejecting the spent bullet casing and subsequently loading a new round into the chamber. Pistols, unlike revolvers, have only one bullet chamber and barrel. The bullets are held in a magazine which is removable and thus allows a semi-automatic pistol to be reloaded very quickly.

The trigger function of semi-automatic pistols is split into two types; the single-action trigger performs only the one action of releasing the hammer to fire the bullet and assumes that the hammer is cocked; double-action triggers will pull back the hammer into firing position and then release the hammer to effect firing.

Semi-automatic pistols are bulkier and more complex than revolvers; the barrel is surrounded and backed by a laterally movable slide. When a bullet is in the chamber and the slide is forward (closed and locked) the firearm can be shot. When the trigger is pulled the hammer hits the firing pin or releases a striker and the bullet is ignited and the projectile shoots out of the chamber and barrel. Using the principles of Newton's Third Law which states that "for every action there is an equal and opposite reaction" part of the energy of the controlled explosion is used to move the slide backwards - opposite to the direction of the bullet. This backward movement of the slide performs 4 main functions, namely

(a) to pull the spent casing from the firing chamber (extraction).
(b) to forcibly remove the brass from the firearm (ejection).
(c) to push a new and unfired round from the magazine into the chamber.
(d) to recock the hammer and / or striker

Because of the differences in operation between the pistol and the revolver the two usually require different ammunition described on the Pistol and Revolver ammunition difference page. An excellent detailed description of the function of the 1911 Colt can be found at 1911 Org - Principles of Operation.