 Some blank firing adapters (BFAs) act as recoil boosters, harnessing the gases produced by the blank cartridge to compensate for the lack of back pressure that would normally occur as the bullet traps the expanding propellant gases until the bullet clears the barrel.This is important on gas-operated firearms, as they rely on tapping some of the pressure built up behind an accelerating bullet moving up the barrel.Without a bullet to act as a "plug", the gases simply rush out the muzzle without generating enough pressure to cycle the weapon properly, since such devices are often fine-tuned to work only within a certain limited range of gas pressures.