Briley will do this, at least according to their website. Gauge to gauge or down one gauge in the case of damaged chamber. I once had a Parker trap gun with the left barrel being rechambered due to a bulged chamber. I sent it to Briley, thinking it needed fixing, and they sent it back saying the gun had been fixed. You cannot tell an insert has been placed in the chamber but you could see a slight bulge on the outside of the chamber from the original incident. Cyril Adams started doing this from 10 to 12. The result being an overbored 12. I have a 10 with a tight chamber that would make a nice heavy 12. Steve Barnett had a couple of the Cyril Adams sleeved guns a few years back. Go for it
