blowbacksystem

A blowback system is a type of firearm action that uses the pressure of the expanding gases from a fired cartridge to operate the firearm's mechanism. This gas pressure is directed rearward against the bolt or breechblock. In a simple blowback design, the bolt is unlocked and free to move rearward once the cartridge is fired. The expanding gases push the bolt back, extracting and ejecting the spent casing. As the bolt moves rearward, a spring pushes it forward again, stripping a new cartridge from the magazine and chambering it. The mass of the bolt and the strength of the recoil spring are critical to ensuring that the bolt does not unlock too early, which could cause a dangerous failure. Blowback systems are often found in smaller caliber firearms, such as pistols and submachine guns, because the lower pressures and smaller cartridges require less mass and simpler mechanisms. Larger caliber firearms generally use more complex locked-breech systems to manage the higher pressures involved. Some variations of blowback, such as delayed blowback, use mechanical means to slow the bolt's rearward movement, allowing for the use of more powerful cartridges than simple blowback would otherwise permit.