How to Build a Pneumatic Cannon
All that you need is PVC parts, PVC cement, and a car tire valve. Some plastic epoxy is also a good idea, to help seal the leaks.
How you build it is up to you, but I like the basic T-shaped design shown here. It’s simple, I find it ergonomic, and it works pretty well. The back end is 3-inch, with two end-caps and a T-connection that narrows to 1.5-in. One of the end caps has to have a valve in it, which can be done by simply drilling a hole and shoving the valve through it. I find that this seal is never very good, and covered mine with the plastic epoxy on both sides. It’s also a good idea to epoxy every joint on the pressure chamber, because PVC cement almost inevitably gets leaks.
The pressure chamber is then connected to a 1.5-in valve, and at its simplest, a 1.5-in barrel that’s a couple feet long, which is perfect for shooting potatoes. I built another gun with that setup, and it can shoot a potato well over a hundred yards, at least by my estimation.
The one shown is more complicated. The valve is attached to a threaded PVC piece. This lets you change out barrels. The one shown is a triple 1-in where two can be open or shut, so it can fire 1 to 3 shots at once. It gets the most distance with only one, but it’s only marginally better than all three. This gun shoots bouncy balls (which have a diameter slightly less than 1-in).
Another good thing about these guns is that they’re pretty accurate. At one point I secured the bouncy-ball shooter to a table, and two consecutive shots went through the same hold in my target. It’s a bit more challenging to aim when you’re holding it, however. They can also be used as water cannons. When they shoot a barrel full of water, it goes about 20 yards and spreads into a nice cloud. Very good as heavy artillery for water fights, except that they’re pretty slow to reload.
And that’s all there is to it, happy building!