Abstract: A detachable large-bore regular barrel of a shotgun is replaced by a light-weight, thin-walled, carrier barrel having a bore in which a smaller-bore tube and an adapter are mounted. This enables the shotgun to fire a smaller-gauge shotgun shell without changing the weight and balance of the gun, since the combined weight of the carrier barrel, tube and adapter matches that of the regular barrel and those parts are designed to provide the same balance. The carrier barrel is provided with the same kind of shell ejector/extractor as the regular barrel. The adapter comprises a tubular member which defines a firing chamber for the smaller-gauge shotgun shell and is disposed in the breech end of the carrier barrel bore, being threadedly connected to the tube therein. The tubular member of the adapter prevents inadvertent insertion of a larger gauge shotgun shell into the carrier barrel and thus provides a safety feature.

Abstract: Two types of choke assemblies are provided to enable a shotgun of specific gauge to be modified in the field to receive a shotgun shell of smaller gauge and also to provide a choke of desired characteristics to suit the needs of the shooter, as for skeet or trap shooting or hunting. Each choke assembly comprises an aluminum tube insertable into the breech end of the shotgun barrel and has integral external bosses to ensure a snug fit. The breech end of the tube is chambered to receive a shotgun shell and the muzzle end of the tube is internally threaded. In one type of choke assembly, a choke is screwed and glued in the threaded tube end at the factory and the entire assembly is installed in the shotgun in the field. Thus, with a plurality of tubes of the same gauge, each would have a different choke permanently attached.