I build all my steel targets out of scrap dump truck frame. Since I build the trucks, the steel is free, but a place that installs dump boxes would have some. Usually the truck frames are too long and you have to cut them. The frame steel is hard, and is 3/8" thick, and can take most handgun loads. I double it up for rifle rounds. I just make shillouttes, 10" X 14" not including the head, and weld some 3/4" rerod on it for legs.