I'm shooting in a 10m range in my basement, very useable, but knocked together with what I had on hand. My backstop/target holder is simply a 3 layer thick sandwich of 2x4's, about 24" square. I staple gun targets to it. It's mounted to the foundation wall (concrete, 14" thick, 1/2" bars @ 12 o/c) with tapcons. This absorbs shots pretty well, though I get the odd roller coming my way with essentially 0 energy.
I've put a few shots into the concrete wall on occasion, and they leave almost no mark. These are CP HP's doing about 900fps. I'm left with about a 1/4" diameter dark ring of lead at the impact point, and a slightly lighter color to the concrete for maybe 1/2" diameter. Just the dark surface concrete blasted clean. No real cratering or indentation. 22 may do more damage, but it seems that .177 at practical power levels do almost nothing.
My setup isn't ideal, a silent trap would be better. It suits me pretty well, tho. The biggest hazard it presents to me is the lead contamination in the target area. Not too worried about that, since the target area is in an old water cistern (thus the heavy concrete), and it's separated from the rest of the basement by a door. Keeps the kid and cats out.
J