Be careful with a Kodiak double rifle when shooting anything but a patched round ball. When the first barrel is fired, the slug can and will move foreward off the powder. If it moves forward too far, the barrel can blow at the breech. I suggest a patched ball only in double barreled muzzleloaders. Slugs can end up getting you and your gun hurt.
: The REAL bullet is quite undersize comparred to most Sniders. Normal is around .586", but like Mar's can be comswaht larger yet. Slugging the bores is necessary. I do hope they are the same.
: I see considerable pitting ahead of the chambers. Firelapping can eleviate that to some extent. Lapping is also useful.