Double action (or double-action) refers to one of two systems in
firearms
A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and operated by an individual. The term is legally defined further in different countries (see legal definitions).
The first firearms originated ...
where the
trigger both cocks and releases the
hammer
A hammer is a tool, most often a hand tool, consisting of a weighted "head" fixed to a long handle that is swung to deliver an impact to a small area of an object. This can be, for example, to drive nail (fastener), nails into wood, to sh ...
.
*
Double-action only (DAO) firearms trigger: The trigger both cocks and releases the hammer. There is no
single-action
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 t ...
function and the hammer will return to its decocked position after each shot.
**Double Action Kellerman (DAK): A variant of traditional double-action used on certain
SIG Sauer
SIG Sauer is since the 1970s a combined brand name of several Firearms manufacturing companies, with SIG referring to ''Swiss Industry Group'' originally founded 1853, while the latter part comes from Sauer & Sohn, founded in 1751 in Germany a ...
semi-automatic pistols. DAK triggers have a long stroke with pull. However, if a user shooting under stress short-strokes the trigger by only releasing it halfway, the trigger will reset, but with a pull. This temporary increased trigger pull is intended to prevent negligent discharges.
*
Double-action – firearms trigger: Pressing the trigger 1) cocks, and 2) drops the hammer. The hammer can also be cocked to fire in single-action (SA) mode.
** With a DA
revolver
A revolver is a repeating handgun with at least one barrel and a revolving cylinder containing multiple chambers (each holding a single cartridge) for firing. Because most revolver models hold six cartridges before needing to be reloaded, ...
, the hammer can be cocked first (single action), or the trigger can be pulled and it will cock and release the hammer (double action).
[Barrett, Paul M. ''Glock: The Rise of America's Gun''. United States, Crown, 2013. 10.] Once the gun has fired, the hammer stays in the decocked position until the hammer is re-cocked (single action), or the trigger is pulled again (double action).
** With a DA
semi-automatic pistol
A semi-automatic pistol (also called a self-loading pistol, autopistol, or autoloading pistol) is a repeating firearm, repeating handgun that automatically ejects and loads cartridge (firearms), cartridges in its chamber (firearms), chamber afte ...
, the initial trigger pull will cock and release the hammer (double action). The
blowback from the firing mechanism automatically re-cocks the hammer after the gun is fired, such that each subsequent shot only requires the hammer to be released (single action). A
decocker, if present on the pistol, can be used to return the hammer to its decocked position to prevent negligent discharges.
References
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