Break open

Break action is a type of firearm action in which the barrel or barrels are hinged much like a door and rotate perpendicularly to the bore axis to expose the breech and allow loading and unloading of cartridges. A separate operation may be required for the cocking of a hammer to fire the new round. There are many types of break-action firearms; break actions are universal in double-barrelled shotguns, double rifles and combination guns, and are also common in single shot rifles, pistols (especially derringers), and shotguns, and can also be found in flare guns, grenade launchers, air guns and some older revolver designs. They are also known as hinge-action, break-open, break-barrel, break-top, or (on old revolvers) top-break actions.

A substantial hinge pin joins the two parts of the rifle or shotgun; the stock with its firing mechanism and the fore-piece and barrel, which hold the round to be fired. In some cases the hinging pin may be easily removable, allowing the two portions of the weapon to be compactly and safely stored. In other cases the hinge will consist of a hook over a pin; releasing an auxiliary latch will allow sufficient travel to allow the hinge to be unhooked.

A latch is operated to release the two parts of the weapon, allowing the breech to be exposed. A shell is inserted into the breech (up to two for a double barreled shotgun and six to eight for a revolver), and the mechanism is closed and latched. The hammer is then pulled back and latched. The weapon can now ready be fired, done by squeezing the trigger.

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Wikipedia