Blowback operation

A firearm operating system in which expanding propellant gases push the cartridge case and bolt rearward, cycling the action without a mechanically locked breech.

Straight blowback: A blowback system in which the bolt is held closed only by its mass and the recoil spring. This is the simplest form: the bolt begins moving as soon as cartridge pressure drives it rearward.
Locked-breech firearm: A firearm whose breech remains mechanically locked during the initial high-pressure portion of firing. Unlike blowback, it uses a locking mechanism to restrain the bolt while pressure peaks.
Submachine gun: A compact, usually automatic firearm designed to fire pistol cartridges. Many traditional submachine guns use simple blowback because pistol cartridges permit manageable bolt forces.
Internal ballistics: The study of projectile motion and changing pressure inside a firearm during firing. Blowback begins with the pressure history inside the cartridge and barrel.
Bolt carrier: A firearm component that houses or moves the bolt during the operating cycle. Its reciprocating mass contributes to delaying breech opening in some blowback designs.
Recoil operation: A firearm operating system in which recoil moves the barrel, bolt, or both to cycle the action. It relies on firearm movement rather than cartridge pressure acting directly on an unlocked bolt.
Semi-automatic pistol: A handgun that uses energy from firing to eject a case, chamber another cartridge, and prepare to fire again. Blowback is common in pistols chambered for relatively low-pressure cartridges.
Cartridge case: The container that holds a firearm cartridge's primer, propellant, and projectile. Pressure expands the case against the chamber while its rear transmits force to the bolt.
Recoil spring: A spring that returns a firearm's moving action parts toward their ready position. It helps return the bolt forward after blowback drives it rearward.
Gas operation: A firearm operating system that redirects propellant gas to cycle its action. It taps gas from the barrel instead of relying solely on case pressure to drive the bolt.

Linked from 7 pages