Method of forming cartridge chambers in firearm barrels

Method of forming a cartridge chamber in the bore of a barrel with a punch having a shank with a free end, a shoulder surrounding said shank and spaced from said end, and a junction between said shank and shoulder, of which said shank is substantially cylindrical about an axis except for being tapered over an endlength to said end, said shoulder lies in a plane substantially normal to said axis, and said junction is of the specified cross-sectional shape of the mouth of the cartridge chamber, with said shank, and junction having a continuous and exposed polished surface throughout, and said shank being intermediate said tapered endlength thereof of a diameter equal to that of the barrel bore, said method comprising forcing the punch with its shank end leading into the bore of the barrel from the butt end thereof until said shoulder rests on the butt end of the barrel and then retracting the punch from the barrel through the butt end thereof, whereby the mouth and peripheral wall of the cartridge chamber are formed into precise form-fit with said punch over its forced contact with the barrel bore, and the polished surface of said shank and junction will, in conjunction with the operation friction between the barrel bore and the shank and junction therein, generate a continuous and uniformly polished surface finish on the mouth and peripheral wall of the cartridge chamber.