BREECHBLOCK
breechblock, breech closer
(noun) a metal block in breech-loading firearms that is withdrawn to insert a cartridge and replaced to close the breech before firing
Source: WordNet® 3.1
Etymology
Noun
breechblock (plural breechblocks)
(firearms) The metal block that closes the breech of a breech-loading gun after insertion of the cartridge.
Source: Wiktionary
Breech"block, n.
Definition: 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withdrawn for the insertion of a cartridge, and closed again before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 Unabridged Dictionary 1913 Edition