Saturday, May 9, 2009

Pedal Gun Fun

Normally when I shoot a postal match, I shoot carefully, use multiple guns, and try to do well. This usually pays off.
Last month didn't work out well for me including rain, snow or both every weekend, and the loss of about 1/2" off the end of my usual trigger finger, so I decided I needed some humor.
I went to the back porch, and dusted off this

which is a pedal-powered air gun. This entry is Class 5, "other". Very much other.

As you can see, the device is made from an exercise bicycle a neighbor up the street was throwing away, the compressor head from a small garage air compressor, and enough PVC to make something almost like a spud gun.

The bottom half of the gun is 4 feet of 2” PVC, capped on the front, and elbowed at the rear. The rear is connected to a 1 in electric lawn sprinkler valve. 24 volt lawn sprinkler valves will work fine on 12 volts DC, and the drill body I used to hold the battery and trigger was $10 at Harbor Freight. The valve is then connected to whatever barrel I’m using on any given day. I have used barrels up to 4 in in diameter, but given the limitations of the valve and the reservoir size, the practical limit is probably 3 inches. Pictured, is 4 feet of 1 in PVC for the barrel.

The projectiles are made from 12 ga shot shell hulls, with the primer knocked out, and the hole threaded for a 1-1/4” ¼-20 screw. Drive the screw in from the front and add a nut on the outside, grind the bolt to a point, and you’re there. I found that heating the open end and pushing it over a conical form expands the hull to more closely fit the barrel.

For you nit-pickey reloading pros, expanding the hull gave me the same result at 20 psi as an unexpanded hull at 25 psi, so 25% improvement, and more stable flight. 20 psi sounds awfully low, and it is, but this thing is efficient enough that if I go much over that, the projectiles go completely through the plywood backstop, and bury the protruding bolt to the brass into my fence.

Pedaling the gun to build air pressure takes less than 2 minutes of easy pedaling to get 65 psi, so 20 psi takes only about 30 seconds or so. 65 psi will punch a really neat 1 inch hole through a sheet of ½ inch chipboard.

In my back yard, I call this a kids toy. In your back yard, I hope your kids are more than 1/4 mile away. :-)

Anyway, I shot the postal match with this. The gun groups about 5 inches at 10 yards, so accuracy is problematic, but I did say I was doing this for fun, right?

Scoring was fairly quirky too. You start with a score of -12 Trillion dollars, as a deficit, and the target modifies this as you shoot. Positive numbers are added to your deficit, and the -1s are subtracted, with the idea being to reduce your deficit. Notice that the positive numbers count as negatives, and vice versa. Also the last 9 zeros have been removed to imbue a false sense of security, much like real life. The above target netted me a score of -68 trillion.

The second target was better, netting me 67 trillion, so I’m reducing the deficit as I go.

The barrel may be changed by unscrewing the one in place, and screwing in something else.
½” tube fits an AA battery, which I haven’t tried.
¾” tube fits ordinary marbles, the supply of which seems to have dried up.
1” tube fits the shotgun shells, and C-cell batteries, which, at 65 psi will go through a cinder block. Also crab apples, especially in groups.
1-1/4” tube will fit a D-cell battery. See above regarding cinder blocks. This has been chroneyed at 600 fps. Also black walnuts.
1-1/2” is a standard spud gun. Break out the spuds, or fallen fruit from trees.
2” fits an empty caulk tube with a 3/8” bolt about 2” long in the front for weight. These babies will fly about 200 yards in a high looping trajectory that kids love, and are stable like lawn darts. Easy to find and recover when embedded in someone’s skull. Also fits rats.
3” fits the small gourds sold around Halloween.
4” fits squirrels. More on that later, maybe. This is also about the practical limit for this device.

Pictured here is a version of the plenum and barrel I set up to try to deal with a surplus of squirrels. It is derived from a similar arrangement a friend used to deal with rats in his factory.

He connected a 2” barrel to a sprinkler valve, and from there to the shop air supply. The barrel was smeared on the inside with bacon, and the assembly balanced so that the open end of the barrel sat tilted slightly down. When the rat ran up the barrel seeking the bacon, the whole thing tilted back, closing the switch for the sprinkler valve, and launching the rat some 15 feet into a brick wall. One weekend resulted in 3 bloody spots on the wall, and the surviving rats cleaned up the rest of the mess. The device was deemed to be so evil that building another was pretty much a moral imperative, so here it is.


Z@X said...

Well I'll be damned. That is pure genius.

Mikee said...

And here I have been using fossil fuels (well, Aqua Net hair spray) all these years in my single shot spud gun. I am humbled.

Mikee said...

Note: The term “Spud Gun” above refers to a device used in accordance with all applicable Texas and Federal laws and regulations regarding the use of unregistered devices of this nature for pyrotechnic use only. Because I think the local gendarmes would look unkindly upon illegal spud flinging, but making loud noises on holidays is perfectly legal. Really, that’s how it works here in Texas. Nobody EVER shoots spuds out of their spud guns. Nobody. Not even my teenage son. Ever.

Billll said...

The authorities are usually more concerned with where the projectiles land than with where they come from, which would account for the booming potato crops just over the border in Oklahoma, southern Colorado, etc. etc.
"Vunce de 'taters are up,
who cares vere zey come down.
Zat's not my department,
says Werner Von Braun."

Kristopher said...


It ain't an NFA device if it doesn't use a fixed cartridge.

As long as the projo and propellant are loaded separately, it isn't technically a "firearm", in the NFA sense of the term.

You can own a replica blackpowder cannon or even a more "modern" Parrot or Rodman gun without a Form 4.

valve actuators said...

More complex control systems using valves requiring automatic control based on an external input require an actuator. An actuator will stroke the valve depending on its input and set-up, allowing the valve to be positioned accurately, and allowing control over a variety of requirements.

Woodswalker said...

I've made something similar to harness the expansive properties of superheated live steam. 4" ID seamless boiler tube 10 ft long, 2" hose to the steam tap on the header tank after the superheater and a ball valve. Stuff a bacon grease soaked rag down the bore, introduce hatch of live trap to muzzle...allow EXCITED, greedy rat to hustle down to breach, elevate muzzle and open valve until rat clears muzzle...usu <1 second.

We used to get over 100 ft out of the average norway rat on the waterfront. This would boost their now hairless pink bodies into the channel where the various scavengers loved the warmed hor dourves....paddle, paddle, schloup and maybe an alarmed sqeak before they shuffled off this mortal coil.