Concrete benches are definitely the way to go. We have a wooden bench down on the primitive range (BP & round ball only) where I do a lot of load testing on weekends with my flintlock rifles. Now and then, I go up to the centrefire range and test, mid week when the dweebs are working; and shoot there off the concrete benches. I use a heavy, normal BR-type adjustable rest for bench shooting, but always rest the gun's stock in my hand, and hand on top of the rest's bag. When shooting on the lower range, I get 1" groups of 5 with the flintlocks at 50 yards and their best loads, but up top on the full-bore range shooting off the concrete benches, those same load's groups shrink to 1/2". That's quite a difference.