justin I am not stating this as fact but I think the way it worked is that the brass plugs they would drop down the barrel (from the breech) had to go a minimum distance into the barrel, say 9". You could have a larger diameter further down the barrel, say .770" just ahead of the chokes. I think you idea of measuring the bore diameter at 9" may be the where the Proof House measured it. They may measure .719" there perhaps the gun is still in proof.
Robert if that .770" is right before the chokes and if the minimum wall thickness is .032" at that point and for the forward half of the barrel and the chamber wall thickness at the forward end of the chamber is adequate I would happily shoot that gun.
Best,
Mike
