You might find this useful. Don't forget to include the weight of the powder charge, it doesn't vanish when burned, it is part of the equation.
Another thing to consider is how much you are fighting the recoil. I remember seeing a 95 pound 13 year old girl shooting a S&W model 29 .44 magnum. While she was fit and using proper form she rode the recoil out and the gun ended up well above the level of her head. A sturdy 230 pound man is going to absorb a lot of the energy that she let be turned into movement, he is going to have much less muzzle rise so the energy that it took to move the gun a foot or so he is going to absorb into the muscles of his hands, arms and back. As I recall, in the video in question the little girl turned around grinning after she emptied the gun and the big guy was rubbing his hand.
I guess I am asking, have you tried limp wristing, it may help.
Blew a disk in my upper back in `82, I hope you can get yourself fixed up or it gets better as you adjust.
Good luck, sounds like you are getting help from the best.