Just to muddy the waters still further, when this gun was proofed in 1872, fractional proof sizes had not been introduced so the 13 proof size stretched from 0.710" to 0.728".
The proof laws that applied when the gun WAS LAST PROOFED (or reproofed) is that which is applied in ascertaining whether a gun is in or out of proof.
So a gun marked 13 proofed in 1874 (before the fractional sizes were introduced) is still in proof at 0.728" but a gun proofed in 1875 (when the fractional sizes had been introduced) would only be in proof up to a bore size of 0.719".
Enjoy!

Last edited by Toby Barclay; 07/13/20 04:22 PM.