What do the bores look like? Are they pitted? If not pitted, are the lands, and grouves simply rounded?

If the bore is pitted, then there is only one way, and that is to sleeve in a new set of barrels! Not cheap, I might add! If the lands and grouves are rounded then they may be the same as when new! Many of the black powder rifles were rifled with Henry, or Rigby rifleing, which looked worn out when new. This rifleing was very popular with target shooters of the late 1800s. The Henry/Rigby rifleing was designed to be used with paper patch lead bullets, and is usually quite accurate. I have a 500/450#1 Express Westley Richards double rifle that was made in 1892 with the Rigby rifleing and it is accurate with paper patched bullets. Most people don't know what they are looking at when they see the Henry, or Rigby rifleing, and think they are worn out. For that reason my WR cost me only $2100us, in it's oak&leather motor case!