I think Researcher once listed early 30's for the Ithaca switch to 2 3/4" 16. Any Flues 16's with 2 3/4", I'd be suspicious of punched chambers. Hunter was about the last company to make the jump. I just sold a 1938 Fulton, and it was still 2 9/16".

Researcher, we posted simultaneously. Glad to see my memory still works fairly well!