There are an unneriving number of youtube videos showing how to make a zip shotgun. It requires a piece of pipe of the correct diameter to chamber a shell, and another that slides over it with a cap on the end and a screw for a firing pin inside. Slide the two pipes together hard enough and it goes off. What happens next is a crap shoot. The gun may go off, or it may just blow up. It seems like buying a real shotgun would be a much better idea, but I don't understand the criminal mind.