Lumps - The projections extending downward from the breech end of a side-by-side gun. Into the lumps are machined the hook (to swivel around the hingepin) and the bites (to accept the locking bolts). Also called underlugs.
Copper Lumps bbls (also called Demi-bloc bbls) - A method of joining the two separate tubes of a set of barrels where the right-hand half of the pair of lumps under the barrels are forged integrally with the right barrel and the left-hand half of the pair of lumps under the barrels are forged integrally with the left barrel. Chopper-lump barrels can be recognized by the fine joint-line running longitudinally down the center of each lump. This method of jointing barrels is the best because: 1. It is the strongest in relation to its weight, and 2. Because it allows the two barrels to be mounted closest to each other at the breech end, reducing problems regulating the points of aim of the two separate barrels
