Wiktionary
underlug
n. 1 (context firearms English) One of the locking lugs on a break-action firearm that extend from the bottom of the barrels under the chamber(s) and connect into the receiver bottom. 2 (context firearms English) The metal shroud underneath the barrel of a revolver that surrounds and protects the extractor rod.
Usage examples of "underlug".
Taurus Raging Bull, a colossal double-action revolver with a molded underlug that made the eight-inch long barrel seem even huger than it was.