Along with stock design and weight of rifle, I'd have to say that weight or rather lack of it, really is the reason for painful kicks. I'v owned and shot a bunch of big bore double rifles and bolt actions and since the heavy ones created less felt recoil, I found them OK to shoot. I have a 10# 338 that I really like to shoot....but since I'm not able to do much anymore, it's going up for sale.
A guy I know had a #1 customized to a 416 Rigby and I vowed that never again would I shoot it. Light weight rifles are for light weight ammo.....and just the reverse is true IMO.
