Geoff’s gun pictures:

[Linked Image from i.ibb.co]
[Linked Image from i.ibb.co]
[Linked Image from i.ibb.co]

I’m thinking the double proof stamp takes us back to pre 1923. 17mm is a 16 gauge, 65mm chambers. Proofed for powder T in St. Etienne.

Good looking old bird gun.

You guys that study the barrel makers can take it from here.
Best,
Ted