Get a good BP cleaner and plastic solvent. Scrub, and scrub, and scrub. Then rinse with hot water and treat the bore with 1000+. And shoot real black powder. Start with 70 grains and go up 5 grains at a time. I have found that those 1-48" twist guns only do so much. If you get a 4" group at 100 yards, that is about it.
Mine like 90 grains of FFFg and a patched round ball.
