Potato Gun

You may want a couple of buddies to go in buying the material with you, or make 3 at the same time, as the pipe comes in 10 foot chunks (enough for three). I bought all material at my local “Home Depot” for about $15.


CHOICE OF MATERIAL
I have seen and heard of plans for spud guns using PVC pipe. In fact, an article in the February issue of “Modern Gun” uses PVC. Some choose to use schedule 40 ABS plastic. The black pipe usually used for sewerage. If you want to know why some choose ABS, take a chunk of PVC pipe. Hit it with a 25 lb sledge hammer. It fragments into many *sharp* pieces. Try this with ABS. The sledge hammer bounces off the pipe and smashes into your foot. But it didn’t break! (The pipe, that is, I don’t know about your foot). PVC also gets brittle with exposure to sunlight. ABS just gets hot. Only ever use schedule 40! That’s the thick stuff. It costs a little more, but not that much more. The bill of material says 10 foot lengths, only because that’s as small a piece as is normally sold.

NOTE: There does seem to be some confusion about what pipe is safest to use. Finding pressure rated ABS pipe is nearly impossible in many areas. Therefore, most spud shooters are constructed of PVC pipe. If you stick to conventional propellants (such as hairspray) and do not use oxidizers, PVC should perform with adequate safety.

BILL OF MATERIAL
1 10 foot piece of 2 inch diameter schedule 40 ABS or PVC pipe
1 10 foot piece of 3 inch diameter schedule 40 ABS or PVC pipe
1 3 inch threaded (one side) coupling
1 3 inch threaded end-cap 1 3 inch to 2 inch reducing bushing
1 2 inch female threaded coupling
1 2 inch male threaded coupling
1 can PVC primer (see NOTE, below)
1 can PVC glue
Sandpaper (see NOTE, below)
Epoxy
1 sparker – I use and recommend an igniter for a gas grill. You can get these at any hardware store.
About 4-6 inches of stiff, solid copper wire

CONSTRUCTION
NOTE: When gluing PVC, it is STRONGLY recommended that you first sand the areas to be glued to ‘roughen’ them. Then use a liberal application of PVC Primer to prepare the area and then glue according to the directions.

STEP 1 – Cut the combustion chamber. Cut a 14 inch section of the 3 inch diameter pipe. You don’t need the rest of the 10 foot length, so save it for future bazookas, or make one with a couple of buddies to split the cost.

STEP 2 – Glue the threaded coupling to the other end of the combustion chamber (using the slip-joint side, obviously) make sure the glue doesn’t run into the threads. This is the rear end of the combustion chamber.

STEP 3 – Glue the 3 inch to 2 inch reducing bushing into one end of the 14 inch combustion chamber. Make sure the joints are clean first and be liberal with the glue. This is the front end of the combustion chamber.

STEP 4 – Prepare the Ross-connector joint (so-named for its inventor, Tim Ross, who modified his gun so he could break it down and pack it in his Miata’s trunk). Cut a 3 inch length of the 2 inch pipe. Glue this into the end of the reducing bushing you’ve previously glued to the combustion chamber.

STEP 5 – Glue the 2 inch male threaded coupling to the other end of the short piece of pipe in STEP 4.

STEP 6 – Cut the “barrel”. Cut a 36 inch (3 foot) length of the 2 inch pipe.

STEP 7 – Glue the 2 inch female threaded coupling to one end of the 36 inch length of 2 inch pipe. This is the joint that allows the gun to be dismantled for storage in your Miata’s trunk.

STEP 8 – Using a file, taper the “muzzle” for the last half an inch on the outside. This will serve to cut the potato as it’s rammed in.

STEP 9 – Prepare the firing mechanism. There are two different ways to do prepare the firing mechanism. I’ll tell you the EASY way first, and then tell you what _I_ use.

THE EASY WAY: You’ll mount the sparker inside the end cap. Drill a hole dead center in the ABS end cap of a diameter to take the shaft of the sparker. Mount the sparker inside the end cap and secure using the epoxy.

MY WAY: First, strip the rubber coating from the last inch or so of the stiff copper wire. Sharpen the exposed end of the wire (if the end is sharpened, the spark is better). Attach the wire to the sparker so that the exposed, sharpened end is about 3/4 inch from the ‘business end’ of the sparker. To attach the wire to the sparker, I used lots of black tape and some epoxy. Next, drill a hole in the sloped part of the 3 inch to 2 inch reducing bushing of a diameter to take the shaft of the sparker. Insert the sparker & wire assembly into the hole and secure using the epoxy.

STEP 10 – Make a ram rod. I used surplus 1/2 inch PVC pipe, 4 feet in length. A broom handle, piece of dowel, etc., will do. Measure and make a mark about 2 feet 8 inches down the ram rod.

STEP 11 – Make sure the glue has “cured”. It is recommended that you wait overnight before firing.

TO FIRE
The Basics: Load ‘ammo’, add propellant, fire!
The Specifics: Remove end cap. Ram a potato from the muzzle end. The tapered end of the muzzle will cut the potato to size. Make sure it has a good seal as you ram it down with the ramrod. Ram to the mark you made. I’ve found most misfires happen when there are gaps between the potato and the barrel where gasses can escape. Spray 2 – 5 seconds worth of cheap hair spray (White Rain, Aqua Net). I’d use an “unscented” one if you can, or the gun stinks after a few shots! Start at 2 seconds and build up! After spraying the hair spray, quickly screw in the end cap. One push of the sparker sends the spud skyward!

SAFETY
Once you shoot this, you’ll see the potato comes out with enough force, you wouldn’t want to be on the wrong side! Usual safety about pointing the muzzle etc. still apply. This is for fun only. I don’t make any guarantee you won’t blow your arse off. (You may laugh it off, however). Personally, I’d never use acetylene, starting fluid (ether), black powder, lighter fluid, gasoline etc. as a propellant, but you may not value your body parts as much. You can get 3 shots off a big spud. Partially baked ones are fun – they seal in better and shoot farther, but they do break up and the barrel is a mess to clean up afterwards.

CLEAN UP
Soap and water. Push a small towel through (here’s a case where it’s OK to clean from the muzzle). I’ve been shooting mine since 12/94 and have been having a barrel of laughs. The spuds will go nearly 200 yards! I plan to make the “220 swift” variety by coupling a one inch barrel to the three inch combustion chamber. I wonder if you put the barrels on threaded couplings you could have interchangeable barrels. Sort of an “Idaho Contender”.

OTHER TRICKS
* Ram in a cardboard container from McDonalds from a large order of fries. Leave the fries in the container. The cardboard serves as wadding and voila! – a shotgun!

* Use something non-flamable as ‘wadding’ (such as a cut out circle of Tyvek (you know, that hard-to-tear stuff that some mailing envelopes are made out of), and then load confetti, a spongy ball, or whatever comes to mind.

* Tim Ross found some CLEAR PVC for the combustion chamber. He reports that there is a really nice pulse of blue light (fire!) when the spud gun is fired.

WARNING
Use at your own risk. If you’re not sure what you’re doing, DO NOT DO IT.

Wear protective goggles and gloves.

These things have a tendency to attract every 8-12 year old kid in the neighborhood.

Be safe and have fun!