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Blowback is a method of operation employed in small arms. The energy required to carry out the cycle of operations being supplied to the bolt by the backward movement of the cartridge case caused by gas pressure when the round is fired, hence the bolt is blown back by the force of firing the round.
Various forms of blowback operation have been developed. Simple blowback allows for a totally unlocked breech, and relies on the mass of the breech block and the strength of the return spring to prevent the cartridge case from coming back too fast after firing. Simple blowback can only be employed in relatively low power weapons and is effectively restricted in use to pistols and sub-machineguns.
Delayed blowback is a more sophisticated form of blowback operation in which the breech is unlocked, but some mechanical delay is incorporated to ensure that the breech block does not move back too quickly. A delayed blowback operation allows the gun manufacturer to reduce the weight of the breech block relative to the weight that would be required in a simple blowback operation gun.
An expensive and sophisticated form of blowback operation employs a locked breech, allowing for the lightest possible breech block, which unlocks at the precise time to allow the residual pressure from firing to blow the breech block to the rear. This system is expensive and also sensitive to variations in ammunition.
Blowback operations are generally cheap, simple and reliable to employ and allow for a rapid barrel changing. However, they prevent power adjustment in the weapon, leave fouling in the breech and are not suitable for use in weapons mounted on vehicles.
 Research Blowback
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Abbreviations
Warfare
