Step 1: Materials
Paper index card
Step 2: Making
Step 3: Shooting
When I tried it, the kickback destroyed the box it was placed in, but this is because I put in some BB's (A major DO NOT.). A copper pipe properly capped at one end works better, but that's your choice.
NOW, PLEASE BE CAREFUL. DO NOT, UNDER ANY CIRCUMSTANCES HOLD IT. DO NOT POINT AT A PERSON OR ANIMAL. TREAT IT LIKE A REAL GUN. Please, be careful. If you do choose to make one, I take no accountability for anything you may do with it. It is not a toy. If anyone is hurt, that's your fault. This is purely educational. DO NOT TRY THIS AT HOME