I just talked with Doc Gary White (owned the old Green River Rifle Works) about this treatment of the Jim Bridger Hawken. He said he has seen hundreds of original rifles of many different schools of building with this muzzle treatment. The Kit Carson rifle is done this way, too. Doc said the GROOVES are deepened by filing a taper back about 3/4" into the bore, then the lands are filed down even deeper at the muzzle to give that kind of gear look. This accomplishes muzzle coning such that a short starter is not needed. I am considering doing this to my Bridger Hawken I just built, but will shoot it as is for a while. To do this, I would make a tapered cone with abrasive paper held on it, perhaps with glue, to cut a 3/4" long cone to just below the grooves at the muzzle. This would give a concentric end to this cone, important for accuracy. Then I would file the lands deeper at the muzzle with a needle file to give that "gear" effect.
