"Nominal" diameter for a 10 ga bore is .775". 11 gauge = .751"
This does not of course prove what any individual gun's bore will measure. No doubt with that very Loooong forcing cone you were getting a lot of gas blow-by using fiber wads. Guns built when fiber wads were the norm generally had short cones.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra