Phil, the JB will turn black with friction (and it will also make brass/bronze bristles turn black). I don't know what your goal was - whether just a good cleaning or you were attempting to lap rough spots from the new barrel - but you succeeded in giving the bore a good cleaning. To try to lap out rough spots would require many more strokes made fast, long, and smoothly. 200 such stokes would probably gain you something in that regard but I would go no further than you already have with a new barrel - the thing may shoot great now.