The Probert Encyclopaedia of Warfare

SINGLE-ACTION

Single-action is a classification of firearms in which the firer manually retracts the hammer to cock it which simultaneously causes the cylinder to rotate. A subsequent squeeze of the trigger is then required to discharge the shot. In a pistol, the term single-action indicates that the hammer must be cocked before each shot. This is usually done automatically by the act of firing the previous shot, but may also be initiated manually and must be done manually before releasing the first shot.
Research Single-Action