I just use odorless mineral spirits. It dissolves the asphaltum completely off the bullet if you leave it in a covered tray. No elbow grease required, but I usually leave things like that for a few days before I come back to look. I always seem to have something else I can be doing, so ignoring them doesn't try my patience. After removing the bullets from the now-colored solvent, they will dry leaving a thin remaining film, but it is harmless. If it bothers you, a second soak in fresh mineral spirits will get it to nearly undetectable levels. If you want a stronger, faster solvent try Naphtha or even the smelly Xylene. One of them will probably get it off, too, though I haven't tried them. I don't believe either is as much of a nervous system threat as MEK or Actetone.
