Back when they were cutting short chambers, shells were paper and the thickness at the mouth was about .025", or about .050 total thickness when considering both sides of the hull. The whole point of chamber length was/is, of course, to make certain the thickness of the hull did not impinge on the bore diameter
Nowadays the mouth thickness of premium plastic hulls is pretty thin, about .005, or .010 for both sides. Unless the forcing cone constricts more than .040 in that first 1/4", there should be more than enough room to safely use plastic hulls in old 2.5 or 2.75" chambers.
If you are superstitious or work on hearsay, , the above absolutely will not work. If the rest of you find fault with this logic, let me know.
