A falling-block action (also known as a sliding-block action) is a single-shot firearm action in which a solid metal breechblock slides vertically in grooves cut into the breech of the weapon and actuated by a lever.
When in the top position, it is locked and resists the force of recoil while sealing the chamber. In the lower position, it leaves the chamber open to be loaded by a cartridge from the rear. After loading, the lever returns the block to the top position to lock the breech in place to seal the chamber. It is a very strong action; when the breech is closed, the receiver essentially becomes a single piece of steel (as opposed to other actions which rely on lugs to lock the breech). This type of action is used in heavy artillery as well as small arms.
Rifles using this action include the M1870 Belgian Comblain, M1872 Mylonas, Sharps rifle, Farquharson rifle, 1890 Stevens, Sharps-Borchardt Model 1878, Winchester Model 1885, Browning M78 and Ruger No. 1. Falling-block action military rifles were common in the 19th century. They were replaced for military use by the faster bolt action rifles, which could reload from a magazine.
As well as artillery falling-block action rifles are still manufactured and used for hunting and target shooting and industrial shotguns (8ga) for shooting clinkers in boilers.
The falling-block action is closely related to the Martini-Henry rifle, the Peabody action (similar to, but not identical with, that of the Martini-Henry), the Ballard action, and the Krag-Petersson (uniquely, a repeater), which use a pivoting rather than a sliding block.