Apparently, the cannon is relatively simple to build. You take a TS8000 propane torch, some flexible, transparent tubing, put it all together, and see what happens. The effect is dramatic, colorful, and very sci-fi. It gets even better when different elements are added into the plastic bottle at the end of the tubing. Boric acid and charcoal seem to produce some of the best effects, as demonstrated in the video.
Describing the first attempt as “not explody enough,” the whole thing is reworked with the aim of using the explosion to shoot something out the end — in this case, a golf ball. Suitable hard plastic tubing replaced the flexible kind, and the golf ball propane cannon was created. In a series of tests, the cannon shoots golf balls with such force they skip across a lake, split a can clean in half, and ruin a perfectly functional tripod.
The contraption isn’t for the faint hearted, because not only is it really quite large, it’s also very loud. The Backyard Scientist estimates it could have a firing rate of 20 balls per minute — and up to a distance equivalent to a football field — and managed to propel a ball some 600 feet in the air.
If the experiment has inspired you to make a propane cannon of your own, then the instructions for making one just like this can be found here.