yep what feltwad said , any losness to the barrles will come to light when you ring them , bad ribs , bad barrels and such .also dont forget to check them for loads , , drop the RR down the bore ..
not alot of original early rifles around but there are alot of shotguns . you start looking and you will be suprised what you find
the Muzzleloader shop has some . there are always some on gun broker or auction arms as well