jrz Dad,
Geo.Newbern is correct, but when you cut it off and "square up" the muzzle,there will be a gap between the barrels, with a rib over and one under it.Plug the gap with a small wad of fine steel wool, 1/4" or more deep, and fill it with epoxy died black, or "Plastic Steel". You can also fill it with solder(Brownell has a "solder black").
Mike