I got a 300 win mag too myself. It doesn't kick nearly as much as a slug gun if I shoot it standing up, but when I tried shooting it on sand bags at a range, man it really hurt bad.
I ended up getting a ridge hunter rest and that took care of most of the recoil, now I can shoot it all day without any problems. The bullets won't really turn the deer into jelly as long as you hit him/her in the ribs, but if you hit the shoulder, it surely will make a big hole and may ruin quite a bit of the meat.