My other hobby besides welding is shooting sports. I was looking on some web page and I saw something called a snail trap. I want to replicate it but make it tons smaller. It is designed for indoor shooting ranges. It works kind of like a one way door. It is composed of a square opening that tapers down to a smaller opening blocked by a one way metal or hard rubber flap. When the bullet enters drum, the flap shuts behind it. The bullet spins around the drum and slows down. I want to shrink it down to a 2'x2' entrance. It needs to survive a .22 LR bullet. Any suggestions on material thickness or does anyone have one of these. I will post pics when I find them.