Dialing in a barrel once chambered isn't the easiest thing to do, but is possible. You can't really cut the tenon off a carbon Barrel like you can an all steel heavy contour, as it'll be too short. His norma improved will clean up the existing norma chamber without a setback, but that is something you'd need talk to him about. You'll likely see a 100fps increase maybe a little more. Is that worth all the time/money for the work and new custom dies, forming brass to the new chamber. That's up to you.