Just a thought, I don't think it would be easy to do or remotely the best way either. The USN converted a lot of their M1 garands to 308 by pulling the barrel and putting in a threaded chamber insert because the regular slide in inserts might come out. Couldn't you just drill out the chamber, thread it and put a threaded rod in there to be your new chamber? At least this way your chamber reamer wouldn't have to touch the chrome bore and you might at worse have to resharpen your drill bit. I think the hardest part of this might be getting the bore in line with the new chamber and your rather long lead before the bullet hits the rifling. I still think you'd be better off sleaveing the outside of a non chromed lined barrel barrel.