Fnord's Piston Hybrid 2.0

_Fnord · Posted: 07/20/2007 7:39 AM Post subject:

Well, here it is (finally).

Fnord's piston hybrid, version 2.0 - aka. "Thunderstruck"

(sorry dialup users)

Prepare for reading.
...

Commence reading:

Here are the basic stats. This stuff is described in detail farther down.
Dimensions:
Chamber volume: 36 cubic inches (around 600 ml)
overall length: 28" sawed-off style
Barrels:
1" x 18" sawed-off
1" x 36" long-gun
.5 x 52" marble barrel
_______________________
weight: 19 lbs (8.6 kg) with sawed-off barrel (!)
mix: up to 4.5x, though as long as ddt doesn't kick in, it could probably do 7x
ignition: flash capacitor+ignition coil setup.(single gap)
universal propane meter
Pimpin' purple propane tank
_______________________
Velocity stuff:*
320 fps with 4oz lead balls, 700-800 ft-lbs
400-500 fps with vaporized potatoes, 700 ft-lbs
900+ fps with marbles. 330 ft-lbs (may have broken mach 1)

*velocity numbers calc'd with evbec.

New features:

Upgraded Valve
This upgrade of my original piston-valved hybrid uses a more efficient, all-steel(ok, so the piston itself is aluminum) barrel sealing piston valve. I've also added an extra port on the end cap for attaching a pop-off valve for easier piston opening, or a high-flow blowgun for pneumatic use. The current pictures show a pressure gauge on this port.

Compacted design
I've reduced the somewhat bulky rectangular look of the last version to a more thin, riotgun-like look.
The entire gun (minus the barrel) can be broken down reasonably quickly to fit in a shoe box.
The propane meter has also been compacted considerably from before.

Better meter
Finally, a propane meter that doesn't leak. Leaking propane has been sort of a curse for me, as there is no way I'm going to give anyone $20 for a $1 tank adaptor fitting. I eventually found an antique(literally) propane/oxy torch and salvaged the usable parts from it.

New handle/stock
New, sturdy grip salvaged from a mig welder. After fighting the spaghetti monster for a while, I got the wiring reloaded into something actually designed for hv. The old hand grip was a spray can gun with a psu power switch hot glued into it. The bad thing about the old version was if you got your hand too close to the charging switch wires when firing, it would arc out of the trigger and into your hand.

Other stuff that hasn't changed:
Ignition
For Ignition I used a camera flashboard and capacitor dumped into a (motorcycle?) ignition coil. The wiring and circuitry is contained within the handle, and the coil and battery are packed neatly above. All the external wiring is inside uber SciFi-looking wire jackets from and old car.
The output voltage is around 35KV (estimated from jump distance).

Construction Materials
The chamber is black iron, and the fittings are all steel(one is brass though). The barrel is also galvanized steel and can be changed in seconds. I'm planning on a breech loading system soon.

Smell
For some reason, this gun has a very unique smell when fired. Something between burning wax/hydraulic oil/black iron enamel. The first time I shot it gave off a puff of smoke like a musket.

History
Even from the beginning, I never expected this gun to work, as I have never trusted my engineering skills with any task more complex than a ball-valve gun. It was constructed for around $40 usd, with most of that being for the large pipe fittings. The first parts were purchased around January (07) and the first real testing was only days ago (6-29-07).

Notes/misc stuff
This gun is more powerful than my 7-foot combustion. At 4x the muzzle energy is the same as a .44 magnum (firing a 240 gr SP).
The sound makes my ears ring, and the recoil is, to say the least, very noticeable. Being that it's a hip-shooter and not shoulder fired, it isn't so bad though.
Marbles give a loud rifle-like crack when fired, so I may be getting past the sound barrier. It's hard to say.
The damage shots I've done are fairly impressive. Bricks get shattered. Plywood gets pwned. Sheet metal is roughly equivalent to tissue paper.
After punching some numbers, I found that this gun is produces about 1/2-2/3 the energy of the mauler at a given mix.
It also seems very convenient not having to change burst disks after every shot. I would recommend anyone with access to a welder/drill press try making a piston valved hybrid over a traditional one. It's so much cooler.

Future upgrades/repairs: needs a more solid propane meter, needs a new rear pressure gauge (the current one couldn't handle the extreme working pressure).
I may also add a small bike pump underneath the chamber.