Larry;
The thing I noted about the 3" shells Bell fired in the 2½" chamber was first, they were low pressure reloads, at least in the article I read, maybe I missed another. As you noted he gave the pressure increase from a 2 3/4" chamber to a 2½" chamber. What he did not give us was an actual pressure when fired in a 3" chamber, thus we do not know how much actual pressure increase he had from the design chamber. In this aspect it all depends upon just how much the cone retards the opening of the crimp. As long as there is clearance between the end of the shell & the cone the crimp can open in a normal manner. Pressure rises "Very Rapidly" until the charge begins to move. It would not take much retardation in the opening of the crimp to prove disastrous. If there is any resistance with a shell chambering fully, "Yank it Out" & find out why. It may just not be fully resized, but if it is being jammed into the cone "Don't Shoot IT" is my advise.
