double-barreled gun
Refers to a firearm with two barrels, typically a shotgun. The term is straightforward and used in contexts like hunting or sport shooting.
He enjoys clay shooting with a double-barreled gun.
Compound of 二 (ni, 'two'), 連 (ren, 'connected' or 'in a row'), and 銃 (jū, 'gun'). The term directly describes a gun with two barrels.