I noticed you mentioned 1 in 48 instead of 1 in 66. Try even less powder. Try 55grs then 60 and 65. 55 of 3f probably wI'll shoot better. Faster twists stabilize balls at slower speeds.
Try .012 and .018 patches too.
Once you got a good idea what it Likes better, then see what it does clean. Take a shot, quickly clean the bore, then shoot, then clean and shoot one more. See what that group is like.
Your shooting open irons. Shoot ywood deer shilouettes at 50 75 and 100. Gives you a very good realistic expecting of where it hits and how the deer look like at those ranges