This is a complicated setup for trying to figure out the best size gun with the right amount of air. I used it to convert my air cannon into a powerful blaster. Follow these instructions and I'll explain everything.

• 1. Measure the inside diameter of your barrel and chamber (printed on outside of the pipe).
• 2. Divide the diameter in inches of the barrel by 2, square it, and multiply by pi (approx. 3.1416), and then multiply it by the barrel length. Do the same thing for the chamber. This number is the cubic inches for that part of the gun, not including fittings, smaller pie, etc.
• 3. Then divide the chamber cubic inches by the barrel cubic inches.
• 4. Now divide the number of psi being used in the gun by the number found in step #3.
• 5. Now subtract the psi being used by the number found in step #4.

This final number should be the number of psi's behind the potato at the end of the barrel. The bigger the number, the faster it goes, and the farther it goes. Here's the setup I used for the air cannon I made before I changed it (with 1-1/2" x 60" barrel and 3" x 36"):

I will use the / symbol for dividing, that's what it means anyways. 1.5 / 2² x 3.1416 x 60 = 106.02; 3 / 2² x 3.1416 x 36 = 254.448; 254.448 / 106.02 = 2.4; 105 psi / 2.4 = 43.75; 105 - 43.75 = 61.25. So there's 61 psi behind the potato at the end.

I really don't know if this works. The chamber is about twice as big in cubic inches than the barrel. And the final number is over 50, so I guess that's what it is. If you need help, give me the size of the pipes and i'll do the rest. What you need to do is try a bunch of different sizes to see what's better. Maybe a longer chamber or a shorter (or longer) barrel. And this works if you use a good sized ball valve (3/4" at least!). The bigger the ball valve, the more air can pass through the valve setup, and more air behind the potato!

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Created 1997-98, Mike Gagnon "Spud Man"

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