Was this gun a 16 bore? How does someone hone .050" and expect there to be any wall left?

Edgar: the 12 over C in the diamond was marked at the time of the original proof. 15/1 however would be considered a 14 bore.

The Proof House once thought a mistake was made, but on further examination found that there was not, nor has there ever been ;)

Thank you, Dr Drew. I missed the sideways 12, but never figured to look for a 12, when .719 is so much smaller.

the 12 over C in a diamond seems to indicate chambers longer than 2 1/2"

12 over C was used starting in 1887 for 2 1/2", 2 5/8" and 2 3/4" chambers. 12 over LC was for 3" chambers
https://www.vintageguns.co.uk/magazi...roof-4-london-

from The Standard Directory of Proof Marks

https://i.imgur.com/HewpVhm.jpg

There is a lot of "supposing" going on here when a wall thickness gauge and a bore micrometer would answer all questions. I would not pass on a 1 1/4 ounce proved English hammer gun without measuring it. They are not that common, but then, Dave Knows that.

Thanks Daryl. I did some more looking. Burrard was no help. We discussed this issue some time ago on DoubleGun and Miller said he'd seen 3" chambered guns marked 12 over C and also over LC.
I couldn't find confirmation but it appears likely the significance of LC changed at some point.
After 1954 there was neither C nor LC, just 12 in the diamond.

Drew, I have a circa 1900 Cashmore Nitro with the 12 over C in a diamond. It is also marked 3" Cases.
Also, here is a Betts with similar markings.

https://i.imgur.com/4urnO7y.jpg

https://i.imgur.com/uPTDU2e.jpg

https://i.imgur.com/12R9d9y.jpg

I think the British enjoyed confusing we Colonials. Your directory suggests that the LC was used only after 1925.
The Betts date code looks to be 'O' for 1934-35

Your Cashmore would be 1896-1904 with the 1 1/4 OZ. MAXM

A 1887 - 1896 Cashmore for 3 1/4" cases marked 12 over C.

https://photos.smugmug.com/Proof-Mar...DSC02195-M.jpg