Your shoulder shouldn't look that bad even after firing a hundred rounds through an elephant gun! Let someone watch you while shooting, I'm 100% sure you're doing something wrong, maybe you get space between the butt plate and the shoulder just before pulling the trigger, there is definitely something wrong with your shooting stance.
Next time try to grab the forearm stock of your sharps with your supporting hand and push forward, when shooting from the bench don't lean into the gun too much, allow your body to move backwards so you can absorb the recoil. If you lean forward too much the recoil will go straight through your body and that leads to bruised shoulders.
For the record, I've fired many .45-70 smokeless loads with a 530 grain postell bullet at about 1500 fp/s off the bench through a heavy single shot rifle, the gun really pushes but I've never found the recoil to be unpleasant. I also never got a bruised shoulder.
(Though the gun makes me cry when I try to shoot it from prone position with the metal butt plate resting on my collar bone