RH, I wish there were a short and sweet answer to your question . . . but there's not. Not all short-chambered 16's are equal. I own a Hunter Fulton from the mid-1930's with short chambers. I don't reload 16ga any more, and I don't hesitate to shoot off the shelf American 1 oz loads in that gun. (If you look back at sources from that period, you'll find that in fact, 1 1/8 oz loads were available in the short 16ga hulls.) But I can vouch that RST's are easier on the shoulder than the WalMart stuff. Generally speaking, I think pretty much any well-made American 16 will work OK with the 2 1/2 DE, 1 oz factory loads--but if it's a light gun like a Sterlingworth with light barrels or an O frame Parker, you're likely to get pretty sharp recoil.
If it's an English or European gun, short chambered, I would not do it. That being said, for a couple of decades I did most of my hunting with a pre-WWII Sauer 16, originally 2 1/2", chambers and cones lengthened. My usual pheasant load was the high brass 3 1/4 DE, 1 1/8 oz stuff. Hurt a lot of pheasants very seriously; did not hurt the gun a bit. Still tight as ever when I finally sold it. But Sauers are pretty much on the "overbuilt" end of European doubles. I've owned some French ones, good guns but lighter than the Sauer and without all those bolts, with which I exercised greater caution. And if I had that Sauer back, I would not shoot American factory 2 3/4" loads in it now.
