[mhardcastle]

I made the potato cannon from this book as a teenager. It was made of a PVC chamber for the propellant and a narrower ~potato-sized PVC pipe with the end filed to be sharp so that a potato would be trimmed down to create a potato slug with no air gaps around it.

The propellant was hairspray. You'd unscrew a threaded PVC end-cap from the back of the cannon, spray the hairspray into it, screw the cap back on, and ignite with a flint striker from the outside.

It was a really cool device.

[pengaru]

Made something similar without a book...

The best was breach loading a racket ball that wouldn't quite fit into the barrel, but would get stuck enough to not fall away when presented forcefully from the larger combustion chamber side.

They flew way farther than potatoes, and exited the barrel with deformations in their ball shape from not quite fitting, making the flight path all sorts of erratic for the first hundred feet or so.

We used to take it to a nearby park and get kids to catch and return fly balls by shooting ~vertically for them. You couldn't even see the ball for a good chunk of the flight, good times. Prolly get arrested for such a thing today.

[plastiquebeech]

Prolly depends more on where you are than when you are.

In a rural area, you're still looking at a pat on the back instead of handcuffs, in the unlikely event that an authority figure notices.

In a suburban area, you get cops asking if you could please stop detonating vegetables near your nosy neighbor's property.

In a dense city, you might be lucky if you can avoid being shot to death after the first few explosions.

[JadoJodo]

I built this exact same thing as a teenager. The “thoomp” was very satisfying. Living in an area with a lot of sage brush made me too scared to try the Cincinnati Fire Kite, though.

[youainti]

Tried that one as a kid when the fog was really thick. Unfortunately couldn't get it to do much more than fall slowly.