One thing to remember regarding JB paste. It's wonderful stuff and I use it to polish barrels, but don't ever expect to push a patch thru with JB on it and have it come out clean. It will always come out dark gray because it's polishing the barrel steel, and is picking up some material on every pass. What I am saying is don't keep polishing waiting for a clean patch, cause it ain't gonna happen. Use it for a few passes and then reclean with Butch's or whatever you like. Look for a clean patch using the solvent, not the polish.
Tom