I would look at pre 1960 loading data where card and fiber wads were used. I load and shoot RMC brass hulls that were made for my chambers. No crimping, instead and over shot card is used to contain the shot. Rocky Mountain Cartridge is located in Worland WY.
I recommend using RMC hulls after using them for over 9 years. The advantage for you would be that most published 2 3/4 recipe for straight walled hulls would fit in a 2 1/2 RMC hull because the hull is the size of the chamber and does not need a crimp. That would include 1-piece plastic wads and/or card and fiber wads.
