the bolt and acts much like a bolt carrier. When the cocking handle is pulled rearward, it first lifts the pawl before retracting the bolt rearward. This system was adapted to recoil operation by Berhnard Müller in his 1902 prototype pistol and has subsequently been used in other pistols such as the Walther P38. Flapper locking (as used in the Degtyaryov machine gun) uses metal plates (pawls) on either side of the breechblock that "flap out" like barbs on an arrow and lock into recesses in the receiver. The flaps can be retracted parallel to the block for unlocking. The straight-pull Heym SR 30 uses ball bearings for locking, similar to an air fitting connector. The Blaser R93, another straight-pull action, is similar. It has a locking collet that consists claw-like segments instead of ball bearings. The multiple claws provide a large contact area to distribute load. These are arranged radially around the axis of the bolt. They extend to lock the bolt by engaging with an annular groove in the barrel behind the chamber and are retracted to unlock the bolt. Blowback Blowback actions use an in-line breechblock in which the breech is never locked and is held closed by spring tension alone. The force of the discharge is contained by a combination of spring force and the mass of the breechblock. They are used in semiautomatic and automatic firearms using low-powered cartridges. It is common in semiautomatic rifles and pistol chambered for .22 cal rimfire cartridges and many submachine guns. A variation is blow forward operation, in which the breechblock is fixed and the barrel moves. Delayed blowback uses additional mechanical devices that retard or delay the rearward movement of the breechblock; however, the breechblock is not locked in place by such devices. It allows a lighter mechanism compared with simple blowback. Floating actions In most longarms, the barrel is firmly attached to the receiver and does not move relative to the receiver during operations. Most semiautomatic pistols firing the higher powered pistol cartridges use a locked-breech design. The action is manually cycled by moving the slide rearward. The slide contains the breechblock and is initially locked to the barrel so that the combined assembly move together. A short movement trips the mechanism to unlock the barrel from the slide assembly, allowing the breech to open. When fired, recoil results in the same action. In many instances, the