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A breechblock (or breech block) is the part of the firearm action that closes the breech of a breech loading weapon (whether small arms or artillery) before or at the moment of firing. It seals the breech and contains the pressure generated by the ignited propellant. Retracting the breechblock allows the chamber to be loaded with a cartridge.
The breechblock is "locked" into the barrel. At the point of firing the inertia pushes the barrel and slide/breechblock backwards together for a certain distance. This type of action utilizes the inertia of the locked together slide/breech and barrel so that its inertia prevents movement too quickly.
The breech block screw incorporates multiple threaded "steppings" of progressively larger radius and a gap step occupying each circular section.A three step breech block screw's circular area would nominally be divided into quarters, with each quarter containing three threaded sections of progressively increasing height and a gap step for insertion.
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 opened (bottom) position, the rear (breech) end of the chamber is exposed to allow ejection or extraction of the fired case ...
A plug-shaped breechblock was screw-threaded so that rotating the handle underneath would lower and raise it for loading with ball and loose powder; the flintlock action still required conventional priming. The Hall rifle: First U.S. cavalry breechloader, originally made in flint but later made-in and converted to percussion in 1830s–1840s ...
Falling block action (also known as a sliding-block action): A single-shot firearm action in which a solid metal breechblock slides vertically in grooves cut into the breech of the rifle and actuated by a lever. In the top position, it locks and resists recoil while sealing the chamber. In the lower position, it leaves the chamber open so the ...
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If the breechblock and barrel are locked for firing but the barrel is not fixed to the body, it is described as a floating action. [1] If the ammunition is caseless, the time required to expel the previous case is removed from the cycle time of an automatic firearm and a higher rate of fire can be obtained than with normal ammunition. [1]