With regard to firearms
, refers to a trigger
that performs one action, namely releasing the hammer
. A single action gun
must be cocked by some other mechanism. On a revolver
, this would be by thumbing back the hammer. On a auto-loading pistol
, the hammer is cocked by the recoil of the slide.
Compare this to the operation of a double action gun which can be cocked and fired by one pull of the trigger.