I've used abrasives and brushes, and prefer the brushes. It is very important to have some way to index the piece uniformly as the work progresses. Trying to eyeball is is a recipe for really ugly results.
Methods aside, engine turning that is done on parts that rub (e.g. the bolt in a M12 pump or the sides of the breech block on an O/U are predestined to show signs of wear or even obliteration. You can re-jewel, but it's going to happen all over again. I prefer to do it right the first time and then let tthe normal wear accumulate as a sign of a gun I enjoy using.
