I shoot a Traditions Deerhunter, probably the most entry level flinter you can shoot. I have had no accuracy problems out to 60 yards with a roundball and patch. 85gr of 2f goex and a .490 roundball. No problems at all. Makes me think it could be the powerbelts. Just my two cents.
Good Luck trying to figure it out, keep us posted!
Good Luck trying to figure it out, keep us posted!