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In 1836, Samuel Colt received a patent for what would become one of the most pervasive and influential weapons in modern weaponry: the revolver. Unlike existing one- and two-barrel pistols that took 20 seconds to reload, Colt's gun with its revolving chamber allowed five or six shots to be fired in rapid succession. Early revolvers were single-action types, but in 1887 Colt was selling its first double-action revolver, nicknamed, according to caliber, "Lightning" or "Thunderer." All single- and double-action revolvers differ in firing operation. Both offer advantages and disadvantages.
A revolver is made up of four main subsystems: frame; cylinder, extractor and crane, if applicable; barrel and sight; and trigger, trigger timing and hammer. The cylinder rotates on the crane assembly, which turns on its own pivot arm in a double-action revolver. An ejector rod passes through the center of the crane and allows the user to eject shells from the cylinder when the cylinder has been swung out of the frame. The cylinder of a single-action revolver cannot be swung out of the frame. The cylinder rotates on a base pin and base pin bushing. The trigger engages the hammer and either raises the hammer to firing position and releases it, or releases an already cocked hammer under pressure of the main spring.
A single-action revolver must be manually cocked by the user before it can be fired. The user draws back the hammer, typically with his thumb, until the hammer engages the trigger. This action rotates the cylinder and brings its next chamber and round into firing position along the axis of the barrel. The gun is now cocked and ready to be fired. Pressure on the trigger will release the cocked hammer; the main spring will drive the hammer forward onto the round in the chamber.
A double-action revolver is cocked by the action of pulling its trigger. The action of the trigger also rotates the cylinder and brings the chamber and its round into the axis of the barrel. Typically, the trigger elevates the hammer to full-cock position, at which point the hammer is released from the action of the trigger and driven forward by the main spring onto the round. Some double-action revolvers are double action only; others can be cocked like a single-action revolver. Double-action revolvers were at first thought unreliable, but Billy the Kid was carrying a double-action Colt 1877 “Thunderer” when he was shot down in July 1881.
Pros and Cons
A double-action revolver can be loaded more quickly than a single-action. Reloading is accomplished by swinging the cylinder out of the gun frame, ejecting all the shells simultaneously with an injector rod, and then using a speed loader or hand-loading the rounds. Reloading a single-action revolver is slower, requiring the user to swing open a gate at the back of the cylinder for each round and then to rotate the cylinder each time to bring the next chamber into line. A double-action revolver can also be fired more quickly than a single-action revolver because the user is not required to thumb back the hammer before each shot. However, the pull weight of a double-action trigger is much greater than the pull-weight of a single-action trigger to accommodate the action of cocking the hammer. The pull weight of a double action can be over 12 lbs., while the pull weight of a single action is often less than 4 lbs. This difference in pull weight leads to decreased accuracy in the double-action revolver.
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