Blowback
Simple blowback operation is where the recoil of the cartridge moves the bolt rearwards to reload the next round. This operation is found in automatic pistols and submachine guns and firearms chambered in lower pressure rounds. The likes of rifle rounds which have higher pressures is usually deemed unsuitable for simple blowback operation. However, there is Delayed Blowback where the chamber is locked until the pressures drop to a safe level to reload.