Firearm action

In firearms terminology, an action is the system of operation that the firearm employs to seal the breech (in a breech-loading firearm), and to load consecutive rounds. Most commonly this is accomplished by means of a breechblock, which reciprocates in the receiver of the firearm. Important factors in the naming of a particular action type depends on how it gets its motive force (i.e. what energy is employed to operate), and how it locks the breech.
The following list shows most of the various types of breech-loading firearms that exist:

Recoil operation

* Short-recoil (Colt M1911, CZ75, Browning Hi-Power, HK USP, GLOCK, M2 Machine Gun, MG42, M82)
* Long-recoil (Browning Automatic Shotgun, Femaru STOP Pistol)
* Inertia-locked (Benelli Shotguns)

Blowback/forward

* Direct blowback (A typical submachine gun, e.g., MP 18, MP 40, Uzi, HK UMP)
* Direct blowforward (Steyr Mannlicher M1894, Hino-Komuro, Schwarzlose Pistol)hgh

Delayed Blowback

* Grooved chamber (Russian Modernized Makarov Pistol)
* Roller-locked delayed blowback (Heckler & Koch HK G3, HK MP5, HK P9, Ceska Zbrojovka Vz 52)
*Gas-delayed blowback (HK P7, Steyr GB)
* Lever-delayed blowback (FAMAS)
* Blish Lock (Thompson submachine gun, i.e. the "Tommy Gun")
* Rotational Hesitation System
** Schwarzlose System (links are rotated by bolt on rearward travel)
** Mannlicher (forced rotation of bolt on rearward travel)
** Modified (forced rotation of barrel on rearward travel, Steyr Mannlicher M1901)
*** Can force rotation counter-torque, or with torque.
*** Barrel can be spring-loaded (use recoil spring) to resist rotation.
* Hesitation Lock (Remington 51)

Gas-actuated

* Short-stroke gas piston system (AK-47, FN FAL, AR-18, HK G36, XM8, MP7, SA80, SKS rifle, et al.)
* Long-stroke gas piston system (M1 Garand)
* Direct impingement (AR-15, M16, AG-42 Ljungman)

Manually operated magazine fed breech loader

* Lever-action (Spencer, Henry, Winchester)
* Rotating (Colt) cylinder
* Pump-action
* Bolt action

Manually operated single-shot cartridge loading

* Falling block (Sharps rifle)
* Falling block (Ruger Model 1)
* Rolling block (Remington)
* Trapdoor (Springfield)
* Break-open (Thompson Center Arms Contender)

Breech loading single-shot without cartridge

* Hall Breechloader used a short breech section that tilted up for reloading
* Ferguson Breechloader used a lever test operated, threaded port, perpendicular to the line of bore
* The Norwegian Kammerlader used a short chamber that tilted up for reloading when operated by a crank.

Muzzle loading rifles

* Matchlock - trigger swings lit match to ignite powder train
* Arquebus - trigger releases mechanical watch spring which rotates steel against flint, creating a shower of sparks, which ignites the powder train
* Snaphaunce - trigger releases spring loaded flint strike steel to ignite powder train
* Flintlock - trigger releases spring loaded flint to strike steel, simultaneously opening path to powder train, to ignite powder train
* Percussion - trigger releases spring loaded hammer to strike cap containing explosive mixture to ignite powder
* Inline percussion - trigger releases striker or hammer to cause firing pin to strike cap containing explosive mixture to ignite powder
* Electrical ignition, selective fire - metal storm

External power

* Gatling action (normally uses crank or electric motor for power, but some Russian designs are gas-operated)
* Chain-powered action

Locking mechanisms

* Rotating bolt (M1 Garand, M1 Carbine, M16, HK G36, AK-47, AK-74, Johnson M1941 Rifle)
* Roller locked (MG42, Rheinmetall MG3)
* Tilt locked (Many Browning designs, FN FAL, FN MAG, Sturmgewehr 44)
* Toggle-locked Luger
* Falling-lock locked (Walther P38, Beretta 92FS)
* Browning Automatic Shotgun, Femaru STOP pistol.
* Radial Locking (Blaser 93)