I lapp them with valve grinding compound and patches. It removes a little at a time and really does a nice job. Also then I do not have to fool around with molton lead. I have a friend that does it the way you described and you're right, it does a great job.

You can fire lapp them as well, but be careful. Just apply valve grinding compound to REAL Conicals and shoot them off with moderate charges. After ten shots, clean the barrel and check the amount of barrel that has been removed. I have never done this, but heard of others doing it...