Decades ago a buddy and I used to go shooting in a old cinderblock/concrete dairy barn, WAY the hell out River Road, paralleling the Potomac river, damn nearly W. VA.......near a then full tilt coal fired power plant, owned by the local utility ......
So we be inside using all sorts of old hay bales and assorted crap behind the targets, and of course.....
TWICE, there was left over bullet copper jackets come bouncing down the length of our 'range'.....along the wall on the left.....hummmmmm.......