450 Ackley.

Sounds like you are having a lot of fun with the bore gun. Can I ask who did the rebarrel job. Obviously they have the 12 bore reamer. I have just bought a greener police shotgun with the view of converting it the same way you have. Have you got a web address for the for pac-nor barrels. My earlier Marlin was not legal for big bore events. Your gun looks great.

Wayne