I have a Joseph Lang and Sons double rifle I hunted with last season and I think you're on a good course...it was a hoot. My rifle was inherited from an uncle that love the old muzzleloader a and this one was in a pretty sorry state when he got it. He disassembled the works, repaired a broken stick, fitted new wood, replaced missing bits, and then re-rifled the bores and re-soldered and regulated the rifle. It ended up at .76 caliber when the rifling finally cleaned up with something like a 1-110" twist. Shoots 700 gr patched round balls with 110gr of old DuPont black powder to point of aim at 60 yards and the flip up leaf sights allow for 100, 150, and 200 yards although I've only shot it to 100. You might consider a quality percussion shotgun that you could build a set of replacement barrels for it too...just a thought.
