The ability to control the amount of recoil is what's really great about shooting muzzle loaders. You can load as much or as little powder as you feel comfortable with.
My oldest son started muzzle loading when he was about 10 or so with a .50 caliber carbine. We loaded up about 30 grains of Pistol (fffg) powder for shooting at 25 yards which proved to be the perfect amount of recoil for a youngster. Then we would load about 40 grains of powder for 50 yard shooting. It was accurate and just enough recoil for him to feel the power without any negatives at all.
I tend to shoot 50 grains of powder at 50 yards out of a light 6 lb. rifle, which are target loads with very moderate recoil.
If I want to shoot farther, I can load up appropriately for that distance and still not wince in pain whatsoever, and I consider myself recoil shy.
High velocity hunting loads with heavier bullets will produce more recoil, and depending on the style of the buttplate or if shooting off of a bench, it can be felt. The amount of felt recoil depends on the bullet weight, powder charge, amount of shoulder padding worn as clothing or the buttplate style, weight of the gun and the toughness of the individual's shoulder.
Some stout loads will be felt out of a lighter carbine but they generally won't hurt much if at all.
I've found that shooting with 777 powder does produce not only higher velocity but a noticiably sharper kick as well. That's why I use it more in the smaller calibers rather than in a deer hunting load. It could be hurtful, but not if a jacket was being worn during the northern winter deer hunting season. But it could affect the amount of muzzle rise and therefore off hand shooting accuracy.
The same goes with shooting bullets that weigh over ~250 grains with 90 or 100 grains of powder out of a .50 caliber carbine, for me anyway. At some point the heavier bullets start to produce more felt recoil than is desired, and that's determined by each individual shooter.
I don't like shooting 300 grain bullets but others can shoot 400+ grain bullets without any felt recoil complaints. So, every person has a different threshold regarding the amount of felt recoil that they desire.
More recoil is sometimes enjoyable for a few shots, but for some, too much recoil for too many shots becomes not pleasurable.
Round balls generally don't produce too much felt recoil on the shoulder except sometimes with 100 grains as mentioned above. But it certainly wouldn't bruise or hurt very much, although it could be "felt".
Nonetheless, many people do like to shoot maximum round ball loads anyway just because it is more tolerable than with the high power centerfire guns.
