Burch,
Short chamber load data is a bit harder to come by than 2 3/4" data. I've taken the path of loading low pressure 2 3/4" shells for my 2 5/8" chambered guns. The number of acceptably (to me) low pressure loads available in the publications I've searched is fairly small. I settled on one for the last few years.
I do have pressure and velocity equipment, but that takes a lot of time and effort to go do the testing to actually develop new loads. I picked one and verified the pressures and velocity in a short chamber gun. I'm happy with changing the shot size for various uses from quail to pheasant. Used it on both, works great.
