Nominal bore dias for 14 & 15 ga's respectfully are .693" & .677". Small end of a 16ga shell is a nominal .732" (.662" bore + .070") Using the same standard a 14ga should be close to .763" or the small end should just about start into the large end of this chamber. I suggest you double check that .708" measurement as that would make the 14 ga smaller than a 16ga. That measurement sounds like that of an 18ga which has a bore dia of .637".

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