Basically, it's just a 1-1/4" Sch80 male pipe coupling to 3/4" FIP adapter. Shove the ball inside the 1-1/4" end, and use a couple to the 1-1/2" pipe over the end. Unfortunately this requires removal of the barrel each time we load a new ball. Oh, well.
The tank is aluminum, and actually from an old fire extinguisher that my father had laying around (for twenty-five years, go figure).
It took a while to locate a fitting that would work in the end of the tank, because it's a wonky thread pattern. I finally found that a CGA580 fitting (used for argon, helium, and nitrogen tanks) fit nicely, but still leaked. At first i tried using plumbing goop, but it leaked after a while.
Then I used epoxy instead. Seems fine up to 140PSI. Before installing the fitting in to the tank, I had my father bore out the inside wide enough to accept a male 1/2" threaded to 1/2" copper pipe adapter, then soldered the two together. Then I added the liquid epoxy to both sets of threads and screwed them together tightly.
While the epoxy was curing, I moved on to the next section, the 'T'. In reality, the 'T' is the body of an over pressure relief valve from an old water heater. I removed the internal of the valve and drilled through the chamber with the largest bit I had, a 5/8". In the end where the lever used to be, I bored out the opening a little more to accommodate a 1/2" Copper FIP adapter, and soldered them together.
After the epoxy cured for 24 hours (just to be safe), I screwed together the 3/4" Ball valve, 'T' fitting, pipe nipple, barrel adapter and the tank assembly.
I actually made my own 3/4" MIP to 1/8" FIP bushing, though I probably could have bought one. But I had the plug, the drill bit, and the tap, so... The second cross fitting is another I made myself. Originally a 1/8" FIP, 1/8" FIP, 1/8" MIP 'T', I drilled a hole in the side and soldered in de-rubbered tire valve. If you decide to solder a tire valve to something, do make sure to remove the Schraeder valve prior to the soldering, and then reinstall when cool. After construction, I assembled the cross with the tire pressure gauge ($4 at Carquest), a plug in one female port (for use later... muahaha!), and screw the whole thing in to the big 'T' fitting. For the barrel, I am using about one foot of 1-1/2" Sch40 PVC. ABS works okay too, but the cheap black coex stuff actually had an oval cross-section and was not suitable for a barrel.
Ammunition:
I like using the yellow foam golf balls from Target, rather than the multi-colored golf balls from K-mart, or nerf balls. They are a little heavier at 12 grams, than the four grams of K-Mart balls and five grams of Nerf balls. But they also fit perfectly in 1.5" SCH40 PVC, where nerf balls want thinwall, and K-Mart balls are smaller yet and want thinwall 1.25" PVC. Target seems to have recently switched from the harder foam balls that I have, to a softer, squishy foam ball. They feel about the same mass, but I have yet to purchase or try any of them to see how they perform.
I need to do a detailed analysis of relationship of pressure to distance for each type of ball I have. So far, at 30 PSI (well within bike or ball pump range), I can get consistent 50-60 foot shots. At 60PSI, I get about 90-100 foot shots. At 130PSI, which is what our shop air compressor runs at most of the time (125-140PSI), the ball goes farther than I can measure.... Let me put it to you this way: My lot is 126 feet long. From the back of the lot at the alley, I can shoot a 12 gram foam ball across the street, beyond the front of the neighbor's house. At LEAST 150 feet. Maybe this weekend I'll take a video of it shooting.
