Re-crowning never needs to be re-cut, unless you wear the muzzle out with a fiberglass rod.
Take your time, use a tapered dowel or even a tpered grinding stone (the type with a shaft for an electric drill) wrapp some emery around it and twist it in the muzzle with your fingers, back and forth, turning the barrel every now and then - then do the other barrel, then finish with the same emery pusing it in with the end of your thumb - rotating the emery and rotating the gun now and then. I poke a piece of cleaning material into the bore to stop the grindings while re-doing a crown.

The whole idea of the crown is to allow the muzzle to swage the ball and patch down to groove diameter without cutting the patch. If the crown isn't quite even, out a thousanth or so, the escaping gas will be on the same side, escaping exactly the same way each time. This consistancy will provide accuracy that is virtually unchanged from a perfect muzzle, as if done on a lathe, then polished by hand. That is how we do new single barrels that aren't breeched with long tangs.
The picture should show the process - easily done perfectly.