The Beaumont–Adams revolver is a black powder, double-action, percussion revolver. Originally adopted by the British Army in .442 calibre in 1856, it was replaced in British service in 1880 by the .476 calibre Enfield Mk I revolver.
Beaumont–Adams percussion revolver
British Army Mark III, Model of 1872
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A trigger is a mechanism that actuates the function of a ranged weapon such as a firearm, airgun, crossbow, or speargun. The word may also be used to describe a switch that initiates the operation of other non-shooting devices such as a trap, a power tool, or a quick release. A small amount of energy applied to the trigger leads to the release of much more energy.
Trigger mechanism in a bolt action rifle: (A) trigger, (B) sear, (C) striker spring, (D) striker.
Thompson submachine gun trigger
The double-crescent trigger on the MG 34, which enabled select fire capability without using a selector switch. Pressing the upper segment of the trigger produced semi-automatic fire, while holding the lower segment of the trigger produced fully automatic fire.