I would contact Greener and get the complete story on your gun if you didn't get it from the previous owner. The wall thickness is much more important along the full length of the bore than it is at the muzzle. Could you post pictures and the serial number of your gun? It sounds like a great eightbore. My Greener Royal eight is #28,804. It's exact weight is 13 pounds, 13 ounces.