to be honest
You don't actually need either. I know, at the beginning it feels like you're getting your shoulder separated from your body, but it's mainly because you're holding it wrong.
I remember Cosmoline saying something to that effect; he had a very good explanation of why the bone-jarring effect occured and a description of how the rifle should be held.
Basically, the butt doesn't go all the way into the pocket the way small cal guns do - you kind of put it on a bit of the pectoral. And, with practice, you learn how to hold the rilfe - not too hard, not too loose, and definitely NOT with the tip of your thumb sticking up or your lips upcurled. Either of those two last ways will result in a bloody mouth or thumb under recoil as your hands or the butt rams into your protruding body parts.
The best position I have found for firing, and I have many MNs, is a kneeling supported position as I firing off a low bench with one arm on the bench (actually on the gun bag) and the right knee in the dirt (actually on top of an empty CZ silvertip blue box).
Each time I go I put about 60 to 100 rounds down range and get about 2" groups at 100 (I'm a poor shot). My favorite MN to do this with is a beat up gunsmith special $150 M39.
After about half a year of shooting I eventually got to a point where I knew how to instinctively hold the rifles. The best part about this is that the knowledge extends to your other milsurp guns, too. I don't feel anything at all now when I shoot 8mm, x54r, 308, 3006, or 3030.
Kev