Ed, of the few issues of DGJ I have, the Winter 2001 one has in it one of the articles by Sherman Bell called "Finding Out for Myself" Part V "Long Shells in Short Chambers".
After extensive testing carried out in a very professional manner he concludes:
"With loads that are sensible in a light 21/2 inch gun, we see no dangerous pressure levels produced. I see no reason, related to safety, to modify an original 2 1/2 inch chambered gun to shoot 2 3/4 shells, If The 2 3/4 Inch Load You Intend To Use Would Develop Pressure That Is Safe In That Gun, When Fired In A Standard Chamber!
I once had the gall to quote said article in the forum you were referred to. I ended up being banned from it after some interchange with pontificating "expert" posters there whose philosophy is of the type: " my mind is made up, do not confuse me with the facts." Apparently they are no longer lurking there.
JC(AL)