Editing Double action (section)

{{for|the system in steam and internal combustion engines|Double-acting cylinder}}
[[File:Fifthchangelock.jpg | thumb | right | A M&P 1905 forth change lockwork with annotations]]
'''Double action''' (or '''double-action''') refers to one of two systems in [[firearms]] where the [[Trigger (firearms)|trigger]] both cocks and releases the [[Hammer (firearms)|hammer]].
*[[Double-action only]] (DAO) firearms trigger: The trigger both cocks and releases the hammer. There is no [[single-action]] 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]] semi-automatic pistols.  DAK triggers have a long stroke with {{convert|29|N|lb-f|abbr=on}} pull.  However, if a user shooting under stress short-strokes the trigger by only releasing it halfway, the trigger will reset, but with a {{convert|38|N|lb-f|abbr=on}} 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]], the hammer can be cocked first (single action), or the trigger can be pulled and it will cock and release the hammer (double action).<ref>Barrett, Paul M. ''Glock: The Rise of America's Gun''. United States, Crown, 2013. 10.</ref> 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]], the initial trigger pull will cock and release the hammer (double action). The [[Blowback (firearms)|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.
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