Making an Air Cannon / Potato Cannon

Could this cannon be converted to combustion easily if you added an ignition source?

please add instructions for both, also item lists.... projectiles?

that was pretty cool, where's the video of firing it, and how much did it cost to make (small one)

Nice cannon. Does it leak at all?

I like your design and your video is well done with the split screen. One thing you might want to consider is using air power with pipe thread tape sometimes causes rusting of the joints and tape failure. This can be prevented by using a pipe thread compound. I used to install high pressure air systems as part of my job and would recommend Loctite Thread Sealant. If you let your system sit pressurized for too long water condensation with introduce the rust to the system. Although depending on how you pressurize the system you may not have moisture problems.