Jim/Miller:

Tried the "gage" again with the 20 rim inside the wall of the crimp area of 12 ga. Remmy Gun Club hull. OD pretty close to .792"<.8" (maybe .797"). Barrels off, lashup under finger pressure seated to expose 12 base rim outside the rim cut. Remmy hull is underlength on nominal by a 32nd so I'd say the end of the chamber is under 2-3/4", probably 3/32nds less= 2-21/32" or nominally 2-5/8". Admittedly a lotta guesstimation.

jack