I am using a 3/8 thick 3'x3' piece of plywood with with a double sheet of 26-Gauge Galvanized Metal Sheet attached to the back, it is held up two plywood wings, in front I can put various targets, which i have at the moment in order of less sound, a plastic box filled with rubber mulch, .22 rimfire rated metal pellet trap with ballistic jelly, and a RX target system of flipping paddles. At 36ft/lb a stray pellet went through the plywood and deformed the steel but did not pass through, so it works for me