Deceleration can be accomplished by unlocking the bolt from the breech and simply stopping the movement of the barrel. This is the method used in the John Browning-designed M1911 ("Colt .45") pistol and the vast majority of modern semi-automatic pistols 9mm and larger (Glock, Smith and Wesson, FN/Browning Hi-Power, SIG Sauer), which are largely derived from his design. In the M1911 a movable link tilts the barrel down and out of engagement with slide recesses. The Hi-Power, Glock and other recent designs simplify this by utilizing a downward-angled ramp on the barrel/chamber which contacts a fixed stud in the frame, moving the barrel down and out of engagement with the slide. In both cases the link or stud also arrest the barrel's rearward movement, with the slide continuing on and extracting the spent case.
Today, the most common short recoil designs where the bolt is accelerated are John Browning's .30 and .50 caliber (7.62 and 12.7mm) M2 machine guns. The .50 caliber M2 is still in wide use in western countries, where it can be found for example on the cupola of the M1 Abrams tank. In the M2 machine gun, a cam track in the receiver moves a rectangular breech lock on a barrel extension out of engagement with the bolt during the first 10 millimeters of recoil. The barrel extension then strikes a short, curved lever which through mechanical advantage accelerates the bolt rearward. The extension and attached barrel halt when the extension encounters a stop, while the bolt continues rearward.
In recoil operation the bolt and barrel are locked together initially. In the most successful deceleration and acceleration short recoil designs, namely Browning's M1911 pistol and M2 machine gun, locking is accomplished by tipping the barrel or sliding a lock vertically in the bolt. In his other designs bolts lock the breech by tipping into receiver recesses. Linear or tilting locking motions rather than bore-axial rotary locking could perhaps be said to be one trademark of Browning designs.
It's perhaps worth noting that Browning was one of the pioneers of automatic firearms. His designs are arguably some of history's most successful. When America joined the fight against totalitarian domination of Europe in World War I, Browning donated his designs to the war effort of the United States, rather than profiting greatly by licensing them. John Browning's deep devotion to the principles of freedom led him to this.
Next Section - Long Recoil
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