Don,
Chuck is right. There are 3 reknown shotgun barrel men that come to mind. I'm not really intimate with their services, but the impression I have is that Stan Baker was a guru of overboring (a lot of skeet guns?), Ken Eyster barrel regulation via choke alteration, and Tom Wilkinson overboring and choking trap guns. I imagine any of them could do it all, that's just what I remember. I had Tom backbore some barrels and the workmanship was superb. These guys are also of the old school of tuning a choke to deliver X% at a certain yardage, et. with a particular load. You might want to just do a search on those names on trapshooters.com for some interesting reading.
Briley Corp has a good rep, but I find it to be a bit large and impersonal for my tastes. I know of too many cases where the "paint job was fantastic, but the wrong color was used."
