Breech plug

(Gun.) in breech-loading guns, the metal plug or cylinder which closes the aperture in the breech, through which the gun is loaded.

See also: Plug

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
Starting with a stock Springfield muzzleloading musket, a portion of the barrel just in front of the breech plug was milled off.
If using an inline muzzleloader, the next step of course is to place a primer (often of #209 magnum size) so that when struck by the firing pin it will explode, throwing enough heat through the breech plug to ignite the powder charge.
The breech plug is a quick-release design, so cleanup is simple.
When cleaning Traditions' Vortek rifles in the past, I've simply opened the action, unscrewed the finger-removable breech plug, and cleaned it by pushing patches through from the breech.
My first model required seating a flanged musket cap over a nipple that screwed into the breech plug. To cock, the bolt was retracted and released once the trigger was pulled.
These take a long time to load, as the gun must be cocked, then each pellet inserted into the breech and pushed home by the breech plug. Finally the breech plug itself has to be screwed tight to seal the breech.
Bolt (threaded spring threads 3/4" retainer bushing) length 7/8" Top capping hole length 1" 1/2" Breech plug and nipple to length 1-1/2" fit No.
It's also equipped with a 1-piece stainless steel Accelerator Breech Plug, which allows you to fire both loose and palletized powder without changing the breech plug.
It has a one-piece stainless steel Accelerator Breech Plug, which allows the shooter to use either loose or pelletized powder without changing anything on the gun.
First you want to make sure that the touch hole is located ahead of the end of the breech plug. Ideally, the back edge of the touch hole would be just even with the face of the breech plug.
A combination nipple wrench and breech plug tool makes removing these a snap then the barrel can be cleaned from the breech as it should be.
The trademark DERINGER PHILADELA was found stamped in two locations-on the lockplate and on top of the breech plug. A letter "P" inside a sunburst was also stamped as a proofmark on the left flat of the breech plug between two bands of gold.