Back by popular demand... the potato cannon webpages! I apologize for the quality of some of the pictures, the pages were originally made circa 1999 when I didn't have a digital camera.
Here are the plans for 3 models of potato cannons. The first model is a simple design and is sort of an economy model. The second model is the mid-grade model, a little more expensive but it is much more versatile. The third is the luxury model, with all the versatility of the second model but featuring built in handles for a more ergonomic design.
The following material is for educational purposes only. I am in no way responsible for your actions, especially damage to property and/or personal injury, should you make a cannon. Please keep in mind that these cannons can be very dangerous and should be given the same respect as a firearm. A little common sense and patience will go a long way.