Labor Day Artillery (Airsoft air Cannon)

School is back in session, and my postings have dropped off. I have, however, finished a few projects right before I went back to school, so some of those will be posted soon. Hurricane Issac screwed up my city pretty badly, and I got a week off school for it. So what did I do? Made an air cannon.
First step was to choose an ammo choice. Airsofters use Nerf Pocket Vortex footballs in their 40mm launchers, which is a little under a 2" diameter. With that in mind, I went to the store.
Three seemed like a good number. They used to be available in lime green and orange with contrasting fins (Which would have been ideal for retrieval in the grass), but now only brown, white and black are available.
At the store, I checked the various sizes of PVC for a good fit. 2" ID won.
The fins need to be trimmed about a 1/4th of an inch. My buddy used a pocket knife so it isn't super straight, but the ballistics don't seem to have been damaged at all.
This is the true gullyworks of the air cannon - The black piece is a sprinkler valve, piloted by a blowgun valve.  The U trap is to re-orient the airflow so the cannon won't be 8 feet long. The air tank screws into the left of the sprinkler valve, and the barrel plugs into the top of the U trap.
As seen before, here's the cannon all layed out. It's a pretty huge air tank, a little bigger than the barrel. I have read that a 1:1-1.5:1 Tank/Barrel ratio is ideal, so I shot for that range. Note that the air tank is schedule 80 PVC, the thicker walled cousin of normal PVC.
And, fully assembled. A scrap of SCH80 was duct taped between the barrel and air tank as a spacer, and the blowgun valve was pulled through. The air tube attached to the sprinkler valve was way longer than I really wanted it to be. Ideally, an air cannon would replicate an RPG-7, LAW, AT4, SMAW, or one of various other military rocket launchers. As a proof of concept, this air cannon was a valuable training aid. Using knowledge and scraps from this one, I can make a smaller cannon with a more realistic appearance. I also have a better idea of how I could make a mortar, or even a towed Howitzer shooting Nerf Mega Howlers.
As for ranges, the first effective shot was at 40PSI, and shot all the way over a nearby building. The estimated range was approximately 200 feet, at about a 45* angle. Subsequent tests have yielded wonderful results at pressures ranging from 20-60 PSI, launching the Nerf footballs an estimated 80 feet straight up. You can even load all three footballs at once, and ranges don't seem to be damaged too badly.

Surprisingly, the Nerf footballs appear to be the weakest part of the design. Pressures of 60 PSI or higher can rip the foam apart. But, soft foam is also a good thing; My car has taken direct hits (And I have as well), without damage. The car was unmarked, and I wasn't even bruised. Shooting footballs in an arc at range would allow you to safely play a great game of long range catch.

I'm trying to find a good location near my school to launch it off. At that time, I'll take and upload a video. Thanks for reading.