I purchased a TC firestorm used and the barrel from the first 6 inches and the bore end for 6inches is badly pitted. The lands and the groove are not in good shape. I've scrubbed the barrel with bore cleaner and brush with no change. Any suggestions.
black powder and pure lead balls are very forgiving. Some pitted bores are actually quite accurate. Others, will tear the patch and throw balls wildly like buck shot.
If you have used an abrasive bore cleaner like J&B, then you won't clean it up more than it is.
Depending on what distances you hunt, consider having a smith ream it smooth. to 54 cal. You get to shoot a larger heavier ball, and with front and rear sights, it is nearly as accurate as a rifle. Still good for at least 75 yds.
I've used pieces of scotchbrite pad and different grades of steel wool. That will at least smooth it out. Even emory cloth works. Some friends ahve brought me a few barrels in worse shape than you described and in taking some time I did get them smoothed out and they seem to shoot well. Good luck.