The patches will come out black, or dark gray, with black streaks from the lands. You don’t clean until this stops, because it never will. All you want is the copper gone, and to see if it is, get all the J-B out with Shooter’s Choice and leave the bore wet for at least 2 hours. At the end of this time run another S-C patch through and see it there’s green or blue on it. If there is, you can do one of two things: Keep up the S-C treatment, which usually takes a while, or go back to the J-B, which is much quicker.