Semi-automatic pistol
A semi-automatic pistol recycles part of the energy released by the propellant combustion to move its bolt, which is usually housed inside the slide.
[4] Most types of semi-automatic pistols rely on a removable box magazine to provide ammunition, which is usually inserted into the grip.
[5] However, some pistols are based on receiver-style designs similar to existing semi-automatic rifles, and thus have the magazine inserted separately from the grip.
[citation needed] Semi-automatic pistols use one firing chamber that remains fixed in a constant linear position relative to the gun barrel.
[citation needed] Typically, the first round is manually loaded into the chamber by pulling back and releasing the slide mechanism.
[7] 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.
[citation needed] A notable exception is the Glock range of pistols, which optimize preset triggers (similar to DAO), but the striker is partially cocked back as the slide closes.
[citation needed] 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.
The Taurus PT145 is an example of a DA/SA weapon, as it has no decocker and thus has its striker primed from the moment of chambering and only enters double-action mode if a round fails to fire upon the pin's impact; at other times, it operates as a single-action striker-fired firearm.
[12] All SA semi-automatic pistols exhibit this feature and automatically cock the hammer when the slide is first "racked" to chamber a round.
[citation needed] The normal mode of carrying an SA semi-automatic pistol is condition 1, popularly known as cocked and locked.
[13] Condition 1 (a term popularized by Jeff Cooper) refers to having the magazine full, a round chambered, the hammer fully cocked, and the thumb safety engaged or on, at least for right-handed users.
During World War II, in the Asiatic-Pacific Theater, an unofficial and unapproved carry mode for the SA M1911 by left-handed U.S. soldiers in combat was carrying the gun with the magazine full, a round chambered, the action in half-cocked position, and the thumb safety (accessible only to right-handed users) positioned in the off (or ready-to-fire) mode.
A self-loading pistol reloads the chamber with a new round automatically each time the weapon is fired, without additional action being required by the user.
In a machine pistol, in contrast, this can be accomplished by blowback, or, less commonly, by gas operation, harnessing gases produced when the gun is fired.
The Desert Eagle is a rare example of a semi-automatic pistol that siphons off some of the gases instead of relying on short recoil operation.
For more powerful calibers such as the 9 mm Parabellum (9 mm) and .45 ACP, some form of locked-breech is needed to retard breech opening, as an unlocked blowback pistol in these calibers requires a very heavy slide and stiff spring, making them bulky, heavy, and difficult to operate.
Browning must be given credit for developing the type of locked-breech action which is commonly used by the vast majority of modern large caliber semi-automatic pistols.
In 1902, Luger's subsequent and similar P08 in 9 mm Parabellum overcame the problem of inadequate stopping power and featured a greatly improved Borchardt-type Kniegelenk ("knee-joint") locking mechanism.
During World War II, Germany was the first nation to adopt a double-action pistol, the Walther P38, which could be carried loaded (with a cartridge chambered) and ready to fire without the risk of an accidental discharge if dropped.
The almost universal trend since the 20th century has been for semi-automatic pistols to replace revolvers for military use, although the transition has been slower in police and civilian use.
