Blowback is a firearm operation that uses energy from the motion of the cartridge case as it moves rearwards by expanding gases created by the ignition of the propellant charge.

Principle of operationEdit

Simple blowbackEdit

Advanced Primer Ignition (API) blowbackEdit

Delayed blowbackEdit

For more powerful rounds or for a lighter operating mechanism, some system of delayed or retarded blowback is often used, requiring the bolt to overcome some initial resistance while not fully locked. Because of high pressures, rifle-caliber delayed blowback firearms, such as the FAMAS and G3, typically have fluted chambers to ease extraction.