According to what I have read in Ned Roberts book, some of those rifles would have had a choked bore, and possibly progressive twist rifling. I am guessing what you have there is a " chunk gun" for shooting off a plank at 60 or more yards. It took me a while to ask what a chunk gun was, a rather unique American match. Dutch Shoultz dry patch method of loading should be ideal for that rifle.

Cheers

Gordon