Another view on this subject is that the short chamber length in the Fox is not enough to make any meaningful pressure difference and the 2 3/4 shells will fit and shoot out of the the short chambers just fine. Before I discovered that there was such a thing as RST or POLYWAD 2.5 inch low pressure loads I shot 'off- the-rack' promotional loads from Wal-Mart in my short-chambered Sterlingworth all the time with no noticeable problems except they kicked too much. The Fox actions were plenty strong, but they're also pretty old now. Shoot 2.5 inch low pressure RST's or POLYWADS if you want, but the 2 3/4 inch RST's will serve you better in the Fox, and they are still reduced pressure as compared to the Wal-Mart loads.
As for the pump-gun, the short chambers usually mean a short ejection port, especially in 16ga. guns. That usually has to be altered to effectively shoot 2 3/4" shells, though it will load and eject 2.5" loads just fine. Make sure your plug doesn't allow more than the legal number of the shorther shells in the magazine.
There is no reason not to shoot and enjoy the short chambered guns you have, so long as they are sound...Geo
