The Probert Encyclopaedia of Warfare

DOUBLE-ACTION

Double-action is a classification of firearms in which squeezing the trigger first causes the hammer to be raised and cocked and - in the case of a revolver - the cylinder rotated before the hammer is then released and the shot discharged, all within a single squeeze of the trigger. This differs to single-action in that the firer does not need to separately retract the hammer before squeezing the trigger.
Research Double-Action