First get some Pyrodex RS, and some bore buttons. The bore button will help protect the patch. Try 70g of powder by volume, and check your patches after you shoot. The rifling may be sharp and cutting them, or you may be getting burn through from the hot powder you are using. If you still are not getting good groups, try using other patching material like denim, and I would try using another patch lube. Try moose milk or Wonder Lube. There are a lot of recipes for moose milk, a good one is; Castor Oil 3 oz.
Murphy's Oil Soap 1 oz.
Witch Hazel 4 oz.
Isopropyl Alcohol (91%) 8 oz.
Water (non-chlorinated if available) 16 oz
Another one I use is Balistol {water soluable oil] instead of Castor oil, Murphys oil soap, and windshield washer fluid instead of the alcohol and witch hazel.
I have never seen a 1 in 48" rifled barrel that will not shoot a round ball well, but some take some work to find the right load. Good luck and have fun.