Short answer. Each barrel is made from a forging. The forging is a solid rod with a "hangy down" lump that looks sorta like a hatchet. The rod portion then is made into the main part of the barrel and the hangy down part is made into the breach and lumps; each barrel is all one solid piece. Two semi-finished chopper lump barrels are joined to make the barrel assembly for a double gun. The chopper term is derived form the look of the rough forging; hatchet = chopper.

DDA