theres a cool site neospud.com
hear is my spud gun
if you reed the instructabule you will learn how. To my knowledge thayer are three types of "spud guns" gas ignition, air ignition, and powder ignition (using black powder and sutch)
well, in the chamber thayer can be ether black powder or a reversed rocket motor, and this has a barrel that would work for that, and is ideal because of a detonator in handle, instead of holding a open flame to the end of the barrel risking burns.
i have a rocket launcher that works under moats principals of a spud gun,. . . i guess