Without knowing the stock design of your gun, there can be lots of other reasons that your load is hurting your shoulder. Where you locate the butt plate on your shoulder or upper arm, in the case of the half moon shaped butt plates, and the width of the butt plate are some of the causes of Pain. Too straight a stock, or too high a comb, can also cause pain, and too much drop at heel can send that stock into your cheekbone on recoil, too. How you hold the stock to your shoulder can also affect felt recoil. Only a Look-see, by a good shooting coach can help you unravel these problems.
Try using 2Fg powder, as RB suggests. I am using 75 grains of 2Fg in my light fowler, and I don't have problems with the recoil. Now, the gun was built to fit me, and that is no doubt a factor is how comfortable it is to shoot. But, there is very little difference between the recoil you will feel using 75 grains of 2Fg, or 80 or even 90 grains of 2Fg. Normally, we don't hear a lot of complaints about the recoil of 80 grains of 3Fg powder in these guns, either. That is why I suspect something else is also going on.
Work on finding the most accurate powder charge for your gun. Those huge pumpkin balls are going through a deer at the short range where you can group RBs accurately, so there simply is no need to use MORE powder, or a faster burning powder to get more "Power". Accurate placement is the name of the game. On a broadside shot, that huge ball will go completely thru the chest of a deer out to 80 yds. using 60 grains of 2Fg.( considered to be a "whimp" load by some of our chest-pounders!)
The "secret" to making meat with these guns is to place that ball accurately so it can do the most damage as its passing through those narrow chests. On a broadside shot, aim just above and behind- ball width-- the elbow on the near-side leg, and you will hit both lungs, and some major arteries coming out of the heart.
I have an Article on the forum, up under " Articles"- ( amazing how smart Claude is in organizing these things:bow: )- in the Member Resources section at the top of the index page to this forum. It may also help you learn how to control any heavy recoiling rifle or shotgun to lessen the punishment to your body.
See: "Controlling Heavy Recoil",
http://www.muzzleloadingforum.com/fusionbb/showtopic.php?tid/222421/