Operation
Typically, the first round is manually loaded into the chamber by pulling back and releasing ("racking") the slide mechanism. After the trigger is pulled and the round is fired, the recoil operation of the handgun automatically extracts and ejects the shell casing and reloads the chamber. This mode of operation generally allows for faster reloading and storing a larger number of cartridges than a revolver, although semi-automatic pistols are potentially more prone to malfunctions than revolvers due to their more complex design and mechanism.
Some modern semi-automatic pistols are double action only (DAO); that is, once a round is chambered, each trigger pull will cock the hammer, striker, or firing pin, and will additionally release the same to fire a cartridge in one continuous motion. Each pull of the trigger on a DAO semi-automatic pistol requires the same amount of pressure. The Kel-Tec P-32 is an example of a DAO action. DAO semi-automatic pistols are most generally recommended only in the smaller, self-defense, concealable pistols, rather than in target or hunting pistols. A notable exception is Glock-brand pistols which optimize preset triggers (similar to DAO) but the striker is partially cocked back as the slide closes. This allows for significantly shorter trigger pulls than DAO. The trigger spring can be replaced with a lighter one and paired with a low-strength sear connector resulting in lightened trigger pulls to improve a shooter's accuracy (like models G34 and G35).
Standard modern semi-automatic pistols are usually double action (DA), also sometimes known as double-action/single-action (DA/SA). In this design, the hammer or striker may be either thumb-cocked or activated by pulling the trigger when firing the first shot. The hammer or striker is re-cocked automatically during each firing cycle. In double-action (DA) pistols, the first pull of the trigger requires roughly twice as much pressure as subsequent firings, since the first pull of the trigger also cocks the hammer (if not already cocked by hand). The Beretta 92F/FS, a full-sized, service, semi-automatic pistol is an example of this style of action. A common mode of carry for DA semi-automatic pistols is with the magazine full, a round chambered, and the gun holstered and uncocked with the external safety unengaged or off.
In contrast, a single-action (SA) semi-automatic pistol must be cocked by first operating the slide or bolt, or, if a round is already chambered, by cocking the hammer manually. The famed Colt M1911 is an example of this style of action. All SA semi-automatic pistols exhibit this feature, and automatically cock the hammer when the slide is first "racked" to chamber a round. A round can also be manually inserted in the chamber with the slide locked back. Then the safety can be applied.
Read more about this topic: Semi-automatic Pistol
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