The multi-groove rifling is similar to that in an Austrian wheel lock rifle I have, about .65 cal and converted to percussion.
That style of checkering is very much like a full stock Michigan (Detroit) made rifle signed "BERGKR". That maker later Anglicized his name to Caspar Berger, likewise I've not seen another of his rifles with that peculiar style of wrist checkering. Additionally, full stock percussion rifles are uncommon in Michigan, most were half-stock.
My opinion, based on this BERGKR/BERGER rifle is that whoever made your rifle was recently arrived here from Germany & hadn't yet fully adopted the American barrel and stock styles. Just a thought..