2holer;
I don't actually have any official specs for a 14 ga chamber & they likely varied a bit from different makers anyway. However nominal bore dia for 14ga is .693. Add to that from .068" to .070" (normal range of froont end of chamber above bore size) & then about .005" per inch for the probable 65mm (2 9/16") chamber length & you sure are hitting right on the .775" diameter they listed as size for rear of chamber. I would say the possibility it was a 14 is very strong indeed.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra