We started with a couple of Hunter sprinkler valves, and I took one and gave one to my brother-in-law, and while I began to fashion my downsized potato cannon, he took on the shoulder-fired route, starting with something that resembled an M79 grenade launcher.
Well, my cannon took a place in my storage room, and my bro-in-law continued developing my nephew's blaster to shoot darts more efficiently, and further to boot.
He modified the Hunter valve by increasing the size of the air passage where the dump solenoid is, and exchanged the solenoid for a faster dumping valve, in this case a automotive shop air gun. This is pretty much elementary for those who make potato cannons like those seen on Spudtech.com.
Camera angle makes the airtank look curved, but it's straight.
The old M79 used to have a self-contained air tank in the shoulder stock, but it was exchanged for a reservoir served by an air tank constructed from 3" PVC, end caps, schrader valve for filling, and an OLD air compressor regulator. 90 psi in the tank yields 45-50 full power shots (10 psi in the gun).
At one end of the tank is the schrader fill valve, but on this end is an adapter leading to the compressor regulator, which really is the key to having multiple shots without the need to re-pump, or dumping the whole load in one honkin' shot. Pressure is set at 10 psi.
We could have used PVC for most of the secondary air delivery and the reservoir on the gun, but my bro-in-law thought that we'd be working with pressures around 100-150 psi, so we'd think to use cast fittings and pipes. We found that 10 psi is ideal and effective for Nerf sized darts, but he left the iron stuff there in case he decided to go with more power!
Here's a close up of the gun. The barrel is brass, about 16" long, and my bro-in-law found it on a dirt road on a quiet Hawaiian island he had been working on. The first thing that came to his mind was the homemade! It's extremely smoothbore, chrome plated on the outside, and required one simple adapter to attach it to the Hunter valve.
The reservoir is 3/4" metal pipe (again, thinking much higher pressures, and thinking safety), with a "T" fitting to adapt the air hose from the regulator to the gun. The gun is held, bazooka style, with the firing hand forward, and the second hand in back holding the hose and fitting. Quite comfortable, actually.
RANGES:
We took some stefans of differing sizes (lengths), and while we didn't do too much measured range testing (on my 400 foot driveway), this piece could consistently hit a coconut tree, 50 feet away from my pool, which is about 60 feet long. They left this with me, so I have it in my posession for some real range testing. I'll try to bump up the reservoir pressure up a bit, while respecting the 90 psi tank pressure so as not to endanger anyone (including me).
As for my homemade? Well, let's just say that I got bitten by the homemade bug again, and I'll get to work cutting up my old design. I have some new ideas, and I'll only say it'll need to be mounted on the back of my golf cart.
Oh, and I'll get back to work on the FAR. (Picked up a new Dremel instead of fixing my broken one.)
-Piney-
