You might be having the problem because of the sand bags. A DR needs to recoil as if you were shooting off hand. The rifle shouldn't touch anything except flesh and bone. Put your hand under the forearm and wrap around the tubes. But nothing except the shoulder behind it. Sticks will help for this.
In my 450 I haven't seen any difference between the 480 Woodys and Hornadys (in 480 and 500) for punching paper.
"When you see that in order to produce, you need to obtain permission from men who produce nothing; when you see that money is flowing to those who deal not in goods, but in favors; you may know that your society is doomed." Ayn Rand
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