This is a rubber-band gun that I made for fun. You can cut it out of whatever thickness stock you want, but I cut mine out of .092 inch Lexan. It is nice and transparent! I used 6-32 x 1/2 inch hardware and put flat washers between the layers.
Cut it out of whatever stock you want. Thickness really does not matter (be reasonable :D)...
Put #6 flat washers between the layers.
Use a small 1 inch diameter rubber-band for the trigger. Just loop it through the trigger and put it on either side of the middle butt stock. I did not put flat washers on that screw due to the thickness of the rubber-band.
Screw it all together and load it up with rubber-bands (It starts to max out at 8, but I imagine if you add more washers in between the layers you could load more on top of the others.).