Pistol slide

The slide is the part of the weapon on a majority of semi-automatic pistols that moves during the operating cycle and generally houses the firing pin or striker and the extractor, and serves as the bolt. It is spring-loaded so that once it has moved to its rearmost position in the firing cycle, spring tension brings it back to the starting position chambering a fresh cartridge during the motion provided that the magazine is not empty.

Through the principles of recoil or blowback operation, the slide is forced back with each shot. Generally, this action serves three purposes: ejecting the spent casing, cocking the hammer or striker for the next shot, and loading another cartridge into the chamber when the slide comes forward.

Once the magazine and chamber both are empty, the slide will lock back, released only when the slide stop is depressed; if a new magazine is inserted before the slide stop is depressed then a new cartridge will be chambered.

Some handguns also utilise the slide stop as a means of releasing the slide, when the slide stop is held upwards for purposes such as field stripping eliminating the need for any further lock mechanisms and the room that these may use inside the gun.

Automatically cocking the hammer or striker is an important function of double-action / single-action pistols. However, some semi-auto pistols are double-action only, and are designed to omit this step (cocking the hammer or striker).

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Wikipedia