Editing Open bolt (section)

{{Short description|System in firearms}}
[[File:MAC10.jpg|thumb|200px|A [[MAC-10]] submachine gun]]

A [[firearm]] is said to fire from an '''open bolt''' or '''open breech''' if, when ready to fire, the [[Bolt (firearm)|bolt]] and working parts are held to the rear of the receiver, with no round in the chamber. When the trigger is actuated, the bolt travels forward, feeds a cartridge from the [[Magazine (firearm)|magazine]] or belt into the [[Chamber (weaponry)|chamber]], and fires that cartridge in the same movement. Like any other [[Semi-automatic firearm|self-loading]] design, the action is cycled by the energy released from the propellant, which sends the bolt back to the rear, compressing the mainspring in readiness for firing the next round. In an open-bolt gun firing semi-automatically, the bolt is caught and held at this point by the [[Sear (firearm)|sear]] after each shot; and in automatic open-bolt fire, it's caught and held in this manner whenever the trigger is released. In contrast to this, in [[closed-bolt]] guns, the trigger and sear do not affect the movement of the bolt directly.

Generally, an open-bolt firing cycle is used for fully automatic weapons and not for semi-automatic weapons (except some semi-automatic conversions of automatic designs). Firearms using [[Blowback (firearms)#Advanced primer ignition (API) blowback|advanced primer ignition blowback]] inherently fire from open bolt only.<ref>{{cite web |url=http://www.quarryhs.co.uk/apib.html |title = OF OERLIKONS AND OTHER THINGS|archiveurl=https://web.archive.org/web/20180831062838/http://www.quarryhs.co.uk/apib.html|archive-date=August 31, 2018}}</ref>