A falling-block action (also known as sliding-block or dropping-block actions) 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 the breechblock is in the closed (top) position, it seals the chamber from the high pressures created when the cartridge fires and safely transfers the recoil to the action and stock. When the breechblock is in the lowered position, the rear (breech) end of the chamber is exposed to allow ejection or extraction of the fired case and reloading of an unfired cartridge. 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 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 typically reloaded from a magazine holding several cartridges.
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.
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