Blowback is a system of operation in selfloading firearms. It uses the energy from the motion of the cartridge case as it's pushed backwards by the expanding gases made by the ignition of gunpowder. Simple blowback systems are found on almost all semiautomatic pistols, with the exception of the IMI Desert Eagle and a few others. Advanced versions of the blowback principle can be found in some machine guns and a couple assault rifles.