How to make a small pneumatic gun out of a pen. It can be pressurized over 100 psi and shoot small nails into wood. THIS IS DANGEROUS if you choose to make this I am in no way responsible if you injure your self shooting it or if it explodes while your pressurizing it.
*I didn't know this but someone has already done a better job of a pneumatic pen on spudfiles http://www.spudfiles.com/forums/pneumatic-pen-gun-project-t7858.html
thanks to Surfguy21 for this info