This cannon is moderately powerful but fun. 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. I will add pictures soon.
Step 1: Materials
Paper index card