It could also be that the gun isn't rifled for ball and patch. I have a .50 cal with a faster twist rate; it won't shoot ball and patch well, but it's as accurate as anything else I own with a 370gr TC Maxi-Ball.Buddy in Colorado has a large bore muzzle loader and tried all kinds of loads and patches and felt wads and other stuff to make it shoot.
It would not shoot at all... talking couch cushion at 50 yards.
I told him to measure the bore and I would make him some leather wads.
When he tried them he no longer hated the gun.
Less than milk jug at 50.