It is noted that 2 3/4" shells were readily available prior to the beefed up loads of the 20's, so the fact an older gun has 2 3/4" chambers is not a guarantee it is suitable for modern loads.
That's a very good point.
Re modern shells in short (or originally short) chambers . . . Bell did record pressure increases of 1,000 psi or more (although most were less than that) when shooting 2 3/4" shells through a pressure gun with a 2 1/2" chamber. By the time you add that potential 1,000 psi increase to the approximately 1,000 psi jump that resulted when we switched from the old shells to the Super-X and its modern counterparts, you're now looking at potentially being 2,000 psi over the service pressure of the shells your gun was designed to handle. The other key issue is that modern shells often have heavier shot charges and higher velocity than what we shot "back in the day". Even the Super-X was only a 1330 fps load. We now have lead "pheasant loads" at 1500 fps. And they're stuffing 1 1/2 oz of shot, or more, into 2 3/4" hulls. In fact, that's probably worse for vintage guns than the pressure difference you get from modern loads in old, short-chambered guns.
