I would start with a pure lead bullet that paper patches up to .487", seated over a lubed felt wad. I had a .451 single barrel that was a sporting/match configuration that as far as I know is still owned by a board member. There was an article written by another board member in the DGJ about how he went about getting his oval bore to shoot.

You might contact the maker, the records still exist.

Firearms imports, consignments


[Linked Image from i.imgur.com]