I was at the school I've been painting for a few months and decided I'd bug one of the electricians for a few spare parts. I grabbed a square electrical box and some electrical box covers. I brought it home and thought to myself, "What can I do with this?" ... So I grabbed some metal tape (duct sealing type with the grey goo on the other side of the metal tape, REAL STICKY STUFF!), and started putting together a .22 trap.
It was actually real simple. All I used was two large electrical box covers, three small electrical box covers, a chunk of steel girder (for reinforcing the back), metal duct sealing tape, some foam rubber pieces, regular duct tape (to cover the box after the fact), and a small piece of welding rod.
I made a crude diagram of how I put it together, and am going to include some pictures of the finished product. For targets I just cut out some cardboard pieces and stuck a few 1" targets from http://www.MyTargets.com
.. I think it came out rather well. And because those electrical boxes are all steel, I know the bullets will stay IN the box. This is a fact that I've tested before, shooting the covers with a .22 from 15 yards with a subsonic load and they didn't even dent, they just made a ding sound and flattened out.
Here's the diagram, pretty crude, but it gives an explanation of why I did what I did. The support rod is two fold, 1) it keeps the walls from moving even the slightest bit, because I also reinforced all the seams where the metal meets with the electrical tape to force it into place, and 2) it keeps the electrical cover I used on the top to cover it from sliding backwards and it gave me a good mounting point for the plate, before I decided to put the piece of steel girder on the back to reinforce the back. As you can see, the back plate is at an angle to deflect the bullet downward into the foam rubber, so it's caught in the foam rubber if there's any kinetic energy left after hitting the back plate.
The parts I used are simply:
And the finished product:
LEGAL DISCLAIMER: Don't do stupid shit. If you put this together incorrectly, or hurt yourself while shooting at it, etc... It's all on you. I did this for my own satisfaction, I won't take the blame if you do some assanine.