If it is REALLY dirty, I'd get some Butch's Bore Shine, and soak it overnight. Then use a benchrest bronze brush, and give it about 10-20 strokes (using a good bore guide), then patch it out with a few wet patches, then a few dry patches. Run ONE patch of Sweet's through, then follow in a couple-three minutes (NO MORE THAN 15 MINUTES for the Sweet's) with a couple of dry patches. If the dry patches show blue/green, you've still got copper in the barrel. Soak it down again, brush it some more, etc...