It wasn't an uncommon practice. The 12 bore gun with 14 bore barrels should be safe with any 12 bore ammunition it was proofed for if still in proof. The photograph shows that the gun is proofed for black powder ammunition. I have seen them marked 15 bore in the barrels; and what about the Vena Contracta gun with 12 bore chambers and 20 bore tubes? No, that is not a gun rechambered to 12, it is a 12 bore with 14 bore barrels. With those wall thicknesses I could see no reason whay it should not stand re-proof for nitro if submitted. If you see the mark 14m on a set of 12 bore barrels that indicates choke i.e. 14 bore muzzle. Lagopus.....
