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 breech-block, 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-actuated
    • Direct blowback (A typical submachine gun)
    • Direct blowforward (Semmerling LM-4, Hino-Komuro, Schwarzlose Pistol)
    • Delayed Blowback
      • Grooved chamber (Russian Modernized Makarov Pistol)
      • Roller-Locked (Heckler & Koch G3 & P9, Ceska Zbrojovka CZ-52)
      • 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)
          • Can force rotation counter-torque, or with torque.
          • Barrel can be spring-loaded (use recoil spring) to resist rotation.
        • Rotating Cam Striker
      • Gas-impingement design (Steyr GB)
      • Delay-block action (Remington Model 51)
    • Inertia-locked (Benelli Shotguns)
    • Short-recoil (Colt M1911, CZ75, Browning Hi-Power)
    • Long-recoil (Browning Automatic Shotgun, Femaru STOP Pistol)
  • Gas-actuated
  • Manually operated (muzzle loaders, bolt action rifles, et al.)

Locking mechanisms
  • Radially locked / Rotating bolt (M16, AK-74, M1942 Johnson, M2 Mauser)
  • Linearly locked (Many Browning designs)
  • Arm-locked (Luger)
  • Falling-llock locked (Walther P38, Beretta M92fs)
  • Browning Automatic Shotgun, Femaru STOP pistol.