Miller,
I seem to recall that the researchers could get a detonation out of a shotgun with an old, factory loaded shell that had been exposed to a lot of vibration, such as rattling around in a cars glove box for years, and then being used. The theory was the powder broke down into dust, which, then acted as an explosive, rather than a propellant.
Looking at that pizza gun give me the willies.


Best,
Ted