I have some experience in the field of potato cannons. MY signature one can be found here
, puncturing a phonebook. The problem with this one is that it is unwieldy (12 feet long at max. length), complicated (many hours of Spudfiles research), expensive ($100-$150), and it takes a while to prep it for shooting (3-5 minutes). In making the apple cannon, I wanted to solve these issues. At the sacrifice of brute force, I believe I have solved these problems. The apple cannon is small enough to fit in an athletics bag to be brought to school with (which has come in use for plugging some fellow ninth graders.) It also needs no peripherals (no pump). I can get off around 3-5 slugs a minute. Finally, it is only made up of 3-4 parts depending on which type you choose to make. All of these parts can be found at any self respecting hardware store.