Noun
The movable piece which closes the breech of a breech-loading firearm, and resists the backward force of the discharge. It is withdrawn for the insertion of a cartridge, and closed again before the gun is fired.
Source: Webster's dictionaryDropping block actions These are actions wherein the breechblock lowers or "drops" into the receiver to open the breech, usually actuated by an underlever. Source: Internet
Break actions main Perhaps the most common type of single-shot action, usually found in shotguns, small pistols, and black-powder "elephant" guns, a break action connects the barrel assembly to the breechblock with a hinge. Source: Internet
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. Source: Internet
Rolling block actions main In a rolling block action the breechblock takes the form of a part-cylinder, with a pivot pin through its axis. Source: Internet
The lever tipped the breechblock including the chamber upwards and back, allowing it to be loaded with powder and ball without the inconvenience of loading and ramming from the muzzle. Source: Internet
The upper rear portion of the barrel was filed or milled away and replaced by a hinged breechblock which opened upward to permit loading. Source: Internet