Bottom line, a REAL Black Powder RB action is plenty strong enough (and than some)for ANY BP cartridge that will fit between it's side walls, and makes up into a nicer looking piece.
Sounds like finding a Swede in a rimmed centerfire would make a better candidate if a fellow was so inclined.
Making sense of the 1867 vs 74 vs 89 vs "whatever other date" is going to take a fair sit down to figure out.
