Before dealing with 2 1/2" shells I'd do some research on low recoil standard ammo, I believe that most ammo makers make them. I shoot nothing but 2 1/2" shells because that is what my guns are chambered for, I reload for them also. A 7/8 or 1 oz shell at 1100 fps will have nearly the same recoil no matter what length hull it is in.
Going to a gas operated semi-auto and low recoil ammo would be a better bet for you
