Heavy loads through light guns off a bench hurt, plain and simple. Higher velocity loads do not help either. This is even more true with fixed breach guns without recoil pads. Couple all the above with a gun and hat does not fit well and/or a poor hold and one will hurt for a while.
To reduce recoil, shoot lighter loads at lower velocities. Add weight to the gun. And a good recoil pad. Do not shoot off a bench, most get too low and too much behind the gun which puts all the recoil on a rigid body. Instead, shoot standing off sticks or a rest. At least use a sitting position. That way your body can move with the recoil rather than remain solidly in place. Use a gas operated semiauto as the recoil is distributed over a longer period of time which makes the recoil seem lighter. Lastly, have the gun fitted to you so the recoil is distributed across the shoulder and into your body as much as possible. It will also put the buttstock more toward the body and not out on the joint.
Another point to consider is muscle mass in the shoulder. When I was younger and better built in the shoulders I could shoot more rounds from heavy recoiling guns than I can now. The loss of muscle mass in the shoulders is probably a major factor.
10 rounds is about the limit of 416 Rigby I can shoot from the bench comfortably and I don't shoot anything more than a 223 before and nothing after. I can do twice that off sticks and still shoot a 30/06 class cartridge from a typical hunting weight rifle comfortably. 10 years ago and a box of 416 off the bench wasn't a problem. Gotta love getting old.
