I would try the copper solvent and JB bore paste. If that didn't do it I would shoot some of Tubbs Final Finish abrasive bullets down the bore. This could help with any roughness too. Then I would treat with Dyna Bore Coat or Tekcrolan Sweet Shooter once it was clean. This can be the Lazerious treatment for bringing a barrel back to life or it will clearly indicate if you need a new barrel.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli