That gets burned, propelling the potato.
Unfortunately the potato gun was doomed by inflation, now as (or more) expensive as sending a 9mm down the pipe.
Back when I was managing MickeyD's there was the Beanie Babies fad and we had them in happy meals(talk about crazy adults!), well one day to amuse my son I stuffed a beanie baby down the tube and let her rip! To my and my son's great amusement not only did it travel a great distance it did so flaming and smoking! We had a lot of fun with those stinking stuffed toys, especially at night

Oh wait, there was a point to that story that tied in to your post.

I remember, you said that potatoes have become as expensive as 9mm, well at the height of the craze those beanie baby happy meal toys were going for $10 to $25 each - just insane! Of course being the store manager my acquisition cost was $0 for as many as I wanted. I also found that my lemon tree also supplied quite good ammunition. Of course California made potato guns, just like anything else fun illegal.