4-5 inches of duct seal putty will stop an 810 FPS / 14.3 gr pellet at point blank range, no problem. Haven't gone above that (yet). I suspect it would stop a 22LR, but haven't felt the need to test the theory. One modification I did make to the nice wooden pellet trap Timmy made for me was to face the front edges with pine quarter round trim with the curve angled toward the center of the target and the headless nails counter sunk. The softer quarter round serves two purposes. It protects the face of the target from not only cosmetic hits, but also from potentially causing the wood to split back to where the grooves to hold the paper target are cut. Second, if shooting wad cutters, the curved face deflects ricochets from wayward shots inward and toward the target face instead of bouncing them straight back at the shooter. Wear those safety glasses anyway. When the quarter round gets too dinged up, I can simply replace it.