Patrick , I do not think I can help with dating except to share some of my info. I have a Grant Side lever that was rebarrelled by Boss. The Boss ( from Ron L) ledger , from 1904 indicates that the customer of the Grant wanted 2 3 /4 chambers for American " case"...I also own a Purdey SBT gun made in 1929 which is also 2 3/4. In the Purdey History by Dallas, there is a brief discussion of the Trap guns being ordered from the US. This was generally though A & F out if NY. Only 59 SBT were made, and I do not know if they were all 2 3/4.
The only picture I have us the one from GI...
Here is a picture of the SBT gun, we ( Bob Beach)know it was ordered though A&F....to a NY order in 1929... Resold though A& F in 1930.
