The first thing I would do is to clean the bore back to raw steel. Use some Hoppes # 9 and swab the bore, then dry patches, re swab # 9 then dry patches. When you get clean dry patches, reswab with # 9 and let the barrel set over night. Reswab with a dry patch next day. You may have to do this for a couple of days. This will dissolve and remove any lead in the bore. Maxi Balls, and Maxi Hunters do have a tendency to lead the bore. I shoot them, and have found this routine works. Next, if possible I would try using Goex. Amazing what a difference in accuracy Goex has over subs. Try shooting 80 grains, and work up loads. I find my T/C Hawkens shoot best at 90 grains FFG. Also let the barrel cool between shots. I find that as the barrel heats up, accuracy decreases. Good Luck !