I finally got my 22lr suppressor and I can finally shoot my M&P22 and Ruger American Rimfire in my backyard without upsetting the neighbors. I'd kind of like to have some way of reclaiming the lead. All I'll be shooting is low velocity and subsonic 22lr, probably at a distance of no more than ten or twenty yards.I don't really want a metal stop because of the noise. (I'm wanting to keep this stealthy and quiet.) I was thinking of a simple plywood box filled with sand. (appropriately covered to keep the cats out of it.) I'd just eventually replace the target side when it gets too bullet riddled. How big or deep would it have to be to effectively (and safely) stop 22lr bullets? Any better ideas for a bullet stop?