My high school friends and I had ample experience with Aqua Net/Butane/Ether/Propane powered PVC 'tater cannons.
As a senior in high school, I was on our schools' State Physics Competition team. The challenge of the competition was to launch a ping pong ball the farthest, no incendiary devices allowed. Ninety percent of the teams, ours included, built a pneumatic ping pong gun out of PVC. Work with what ya know right?
We came in 3rd, we should have won, since the only 2 teams that beat us didn't follow the rules. The rules explicitly stated that the ball couldn't have anything on/attached to it. The teams that beat us, and a few of the others poured various lubricants down their barrels, mostly vegetable oil, after loading the ping pong ball, so the ball came out covered in oil. That was almost 20 years ago, but I'm not still bitter, no really.
There was a lot of math involved, for the ideal barrel length, psi, etc. to satisfy our physics teacher, but we did all of the construction, and most of the testing at my grandpa's shop/barn. We destroyed and/or dented a lot of ping pong balls in testing. Grandpa had a cattle farm, and his own vet cabinet with various things you'd need for maintaining a healthy herd of cattle, including some large syringes. I got the bright idea, of using a syringe to fix our dented ping pong balls, which worked great. Then I thought, "hey, if I can put air in these, I can put something liquid in them too." I then proceeded to fill ping pong balls with water.
No exaggeration, or hyperbole, somewhere, way out in the woods, at least 1/3 mile away, due North of the sliding doors of grandpa's shop are a pile of water filled ping pong balls. Based on their trajectory when we lost site of them (orange ones were easier to track) I wouldn't be surprised if they're even further out.
After the competition, I became the custodian for the ping pong cannon, and all kinds of stuff were launched out of it. We discovered that Key limes are roughly ping pong sized, and proceeded to splatter green citrus everywhere. Then one of us got the idea to freeze some limes... 120 PSI frozen Key lime out of a "ping pong gun" will go right through a cinder block wall.
There's plenty more stories, but I don't need to incriminate myself any further.