I'm not sure about when the 20's had the 2 3/4" standard. But Hunter Arms didn't switch over to 2 3/4" for the 16ga until very late in the 30's. Maybe not until 1940. Someone may have a more exact date. But Brophy's LC Smith book (p. 228, Appendix C) shows a schematic for Elsie barrels, and the 16 is shown to have a short chamber. Date of that drawing is April 1938.