I wonder of there is any data on old english RR over on that gourmet shotgun site?
I just queried my FF'n buddy who has quite a reference library on the antique aspects of that sport.
I've seen Purple-heart in a local woodcrafting shop (Johnsons Workbench) I visit to get my sawdust & tooljunkie fix. It might make good lathe turned RR for a fancy set of cased pistols, like the colored ebony, rosewood etc; but the stuff I've seen had a lot of exotic crazy grain and, while heavy, looked a bit brittle for a working ramrod for a long gun.
I'd think pushing a tight patched ball down a long, possible dirty, barrel mandated a pretty specific set of specs to do it well and safely.