The science fair was at the White House today. Fun was had by all.
I think that would work even better if you added a squirt of butane and a spark in there with that compressed air. I did some ambient pressure, propellant fired PVC cannons and hand guns back in the '90s. I showed one to my dad's Rotary exchange student from Norway who stuck around after his year to get two EE degrees from Georgia Tech. I think he was in graduate school when I went through my spud gun phase. It was Thanksgiving and we were heading back to visit the parental units for the holiday. I was taking the spud gun to show it off for my dad and brother. We stopped at the grocery store to get some ammunition. Arne was impressed with the sweet potatoes for $0.49/lb. "They have armor piercing qualities!" he exclaimed. Immediately after we fired the spud gun at my dad's farm he wanted to go to the hardware store to get parts for a larger bore model to see if he could shoot a potato clear across his pond. That's when I got into making 1/2" PVC pistols. The waste from the potatoes in the big gun provided up to 6 more shots in my little pistol! I was into the conscientious use of resources even back then.
After Arne got back to Norway he made his own spud gun but he added a compressed air component. We'd looked up the combustion characteristics of the hair spray we were using to fire it and realized the problem was most people were using too much propellant for the amount of air they had. So Arne added a Schrader valve to his and pumped it up with a bike pump after squirting in the propellant. He said the performance was very good.
I actually sold my first spud gun to a UGA grad for $30. If you went to Georgia Tech you'd get what's funny about that. What's the statute of limitations on unlicensed weapons trafficking?