openbolt

Open-bolt refers to a firearm action in which the bolt is held rearward in the receiver when the weapon is not firing. In an open-bolt design, the chambered round is exposed to the breech; when the trigger is pressed, the bolt moves forward under spring pressure, chambers a round, and the firing pin on the bolt ignites the cartridge as the bolt continues its forward travel. The breech is not locked closed during firing, which is characteristic of many blowback-operated designs.

Open-bolt designs are typically contrasted with closed-bolt designs, where the bolt is in battery and a round is already chambered when the trigger is pulled. The two arrangements have different implications for accuracy, cooling, recoil, and safety. Open-bolt systems can simplify the mechanism and provide rapid cooling of the breech, but they generally sacrifice aiming stability and can produce more muzzle flash and noise compared with many closed-bolt equivalents.

History and usage vary by context. Open-bolt configurations were common in many early automatic firearms and submachine guns due to their simpler construction and cooling advantages. They remain in use in some older designs and, in contemporary contexts, in certain airsoft and paintball markers that employ blowback operation. In modern civilian markets, closed-bolt designs are more prevalent for precision and safety considerations, and open-bolt offerings are often subject to specific regulatory rules in some jurisdictions.

Examples of open-bolt applications include various historical submachine guns and current non-firearm replicas or markers that utilize blowback mechanisms. See also: closed-bolt, blowback operation, submachine gun, airsoft marker.