I have a Savage 300WM that came with the tupperware stock. For me what I noticed most, was the tendency of the gun to jump up when shooting off the bench, not so much the recoil itself. I prefer when shooting off the bench and a rest to have my left hand back under the rear of the stock, but that's not a good idea with a light magnum gun. I found that I needed to either grip the front of the stock to hold it down, or have the hand up front pulling down on the sling to catch it from jumping up so much.
If you add any weight, such as loose lead shot in a bag, make it removable. You won't want or need that weight in the field. With a shot or two at game and a jacket on in the fall, you won't feel a thing. Its at the range when the weather's warm and you are just wearing a T shirt that it might start to get at you.