I've done it to 3 45 LCs to remove the constriction at the threads where the barrel screws into the frame. Also did it to a 45-70 to remove a constriction under a dovetail cut. Do some looking around at the Beartooth Bullet site.
Quote:
However, he also concedes that fire lapping INCREASES THE DIAMETER OF THE THROAT. And given that most all throats are cut larger than they should be, especially from factories, my contention is that while you may make temporary improvement in accuracy fire lapping existing barrels, you also wipe out potentially thousands of rounds of throat life by further enlarging it fire lapping.
http://www.bellmtcs.com/FAQ/Fire_Lapping.htm
What are you trying to achieve Pete? Neither of those are what I would call real shooters.
A liberal amount of JB bore paste maybe a better alternative.