Episode: 536
Title: HPR0536: Spud Guns
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0536/hpr0536.mp3
Transcribed: 2025-10-07 22:41:59

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Hello and welcome to Hacker Public Radio. This is your host, Alal.
And today I'm going to be talking about Spug Guns.
This is my first time doing a show actually, so hello everyone.
I just started listening to Hacker Public Radio a month or two ago and very impressed with it.
And so I thought I'd contribute something back.
I think everyone knows what a Spug Gun is.
But in case you don't, a Spug Gun is a homemade weapon used for launching potatoes for fun.
Or some airport ones are used for launching t-shirts into crowds at events or hot dogs or other promotional things.
And the amphima actually uses them for testing buildings for tornado resistance.
They don't get tornado certified until they can withstand a 2x4 launch start of a air-powered, not a Spug Gun, but something based on the same design.
Until they can withstand that being fired at their walls.
So, first of all, as with anything like this, you didn't think you could escape a disclaimer.
Did you? Well, the following is not a really professional one.
It's just one that I made up, but I think you'll get the point.
The following information is for informational purposes only and does not pretend to be complete or accurate.
None of the materials used are recommended by their manufacturer for the purpose they are being put to.
Failure, malfunction, or misuse of the project can result in injury or death.
And so neither eye nor hacker public radio can take responsibility for damage to person or property caused by this information or the use of it.
If you do go against my advice here and build a Spug Gun, please go first to one of the resources that I'm going to give you and get detailed and complete visual plans and information.
This is important because, as with anything visual or mechanical, it's kind of hard to figure out exactly how to do something by a description.
How big is this? Does it go here or there?
And it's a lot easier to just go from a picture rather than from a description.
Same as it's kind of hard to remember all the commands and a command of the week or something from a description, so it's put into the show notes.
Also, where I live, you can do anything you want with Spug Guns, but that's not true around the world.
So you're responsible for finding out what your local laws are in regard to them.
Some places go all out and just let you do anything like where I live while others totally outlaw them or place a restriction on the total energy of the projectile
or make you get an actual firearms license to possess and use these or any combination thereof.
So you've got to find out what your laws are before trying to use this.
I mentioned that in making a Spug Gun you are using materials in a way not recommended by manufacturers.
The biggest place where this is the cases in the use of PVC pipe, most Spug Guns are built out of PVC tubing.
Couple are built out of aluminum pipe or even copper pipe that's pretty expensive or steel pipe if you can find it and work it.
But PVC is the very much most used material with ABS plastic also being used.
The biggest problem with PVC is that when it fails, catastrophically fails as it explodes, it sends out a lot of shrapnel, so be warned.
There are two basic types of Spug Guns. There's the Combustion Powered One and the Compressed Gas Powered One.
Combustion is the simplest so I'll talk about that first.
There are three basic parts to Combustion Spug Gun.
There's the barrel section of PVC pipe, the Combustion Chamber, larger section of PVC pipe, and the igniter, which is either a flint type removed from a lantern or bought new as a lantern igniter replacement, or there is the PCO electric type such as this found in barbecue grills.
Both of them work, both of them are used.
The flint igniter is easier to work with, but the PCO one is easier to use once you have it mounted because it's a simple push of a button rather than spinning a knob.
With a Combustion Spug Gun, the propellant is generally the aerosol from a can of deodorant or hairspray.
If you look around on the internet, you'll find rate guard recommended, rate guard deodorant is very good and possibly the best propellant for a Combustion Spug Gun, while besides propane and stuff like that, but we'll get into that later.
But apparently from what I've read, it has been reformulated in such a way that it is no longer flammable or the aerosol isn't flammable anymore, which you aren't actually using the deodorant product.
But that is pretty much wasted money as far as Spug Guns are concerned.
What you're after is the propellant gases that shoot it out of the can.
These are a mixture of highly flammable gases such as propane, methane, butane, stuff like that.
So when they're mixed with air, they burn pretty well.
Actually, kind of fun thing to do to prove this to yourself is you take a candle, light it, and making sure you're somewhere that you don't have anything that you want to burn up anywhere near.
Take the candle and you take a can of aquanet hairspray or something like that and spray it over the top and you'll get this nice, like, not a blowtorch.
Blowtorch is mixed in such a way that it burns really clean, but this really noisy and exhilarating flame shooting out of the end of your can of hairspray or whatever.
So deodorant hairspray is used as fuel, of course, oxygen in the air around us as the oxidizer.
One other interesting thing to note with combustion Spug Gun fuels is that when you're buying deodorant or hairspray, more expensive isn't better.
Actually, the cheaper, the better, because while, like I said, you're after the aerosol, not the actual product.
Now before we move on from combustion Spug Guns, I'm going to give you the basic plans for building one as far as I can convey them over the air.
Again, these are four informational purposes only, but I would just like to demonstrate how ridiculously simple it is to build a combustion Spug Gun.
What you need following the plans that I have from the book back here, Ballistics, is as follows.
36-inch length of 2-inch PVC pipe, 14-inch length of 3-inch PVC pipe for the combustion chamber, 3-inch to 2-inch reducer to go between the barrel and the combustion chamber, and 3-inch coupling with one side threaded.
So that's basically a thing that sticks on to the end of the 3-inch chamber, which is threaded to take an end cap, which is the last item, or the last PVC item, a 3-inch diameter threaded end cap.
You also need a sparkler assembly, which can either be flint or PVC electric.
To assemble these components, you cut the PVC to the length specified, prime and glue the ends as per good PVC solvent welding practices, and you take and file around the end of the barrel.
Basically, put an edge on the end of the barrel. The reason you do this is this is called a potato knife.
So when you take a potato, so of course not going to fit exactly in the barrel, but if it's a little bit bigger, you push it down on this sharp end of the barrel, and it will cut off the excess potato and leave you with a perfect plug already in the barrel and ready to be rammed home.
So you solve them well, this is what it's set for 24 hours, and one other good idea is I mentioned that when PVC pipe fails, it creates shrapnel.
I haven't done any testing to find out what actually happens, whether this actually helps anything, but it seems a good idea to wrap it with some sort of tape, such as, say, mailing tape or duct tape,
to kind of contain it and give added strength to the barrel. At least I've done this with all Spugguns that I've built so far.
I know people who haven't, and they've been just fine, so just an added precaution.
Another thing to watch out for with PVC pipe is you don't want to get cellular wall PVC pipe.
This is kind of an insulated PVC. It has this kind of foam stuff in between two layers of hard PVC, and though I've used a gun that is built with this,
I've heard that it will fail eventually, and it's really not a good idea to use this, especially since it's more expensive and worse at the same time.
So once you have this built and cured, the operation is as follows. You procure a bag of potatoes that are at least two inches in diameter, and a can of, say, aquanet hairspray.
Like I said, breakguard was preferred when you could still get the flammable type, especially because it doesn't gum up your gun like aquanet does or like hairspray does.
But right now hairsprays probably one of your better bets, though, of course, with what these stupid things cost experimentation is pretty easy and cheap.
So you take the hairspray, spray it in, count to two or three seconds to get the proper amount in.
If you get too much in, you can just air it out if you get too little in. Same thing.
And then you screw in the cap quickly before the gases can flow out and twist the, well, it's not so much a twist, it's like a flick.
Just spin the igniter as fast as you can, assuming that you've used a flint igniter.
And that will create a big shower of sparks inside the chamber, and hopefully a miniature explosion, which will send your potato flying through the air.
You don't have to strain yourself to potatoes, either. I've heard of wimes being used. I've personally used apples, which seems like a sad waste of such a good fruit.
But if you have a tree of wild apples growing around your place, they might actually be easier and cheaper to get them potatoes.
The origins of Spugguns have never been really found out. It's such a simple thing that when a person made the breakthrough probably didn't even think about writing it down.
But from all that I've heard, probably the first projectile used in a weapon which would be recognizable as a Spuggun would be a tennis ball, which also work well if you can find the right size pipe.
Okay, so that's the combustion Spuggun. The second major type is the airport one.
These have the same type of barrel as a combustion gun, but rather than an attached and directly linked combustion chamber, they have a sealed air chamber.
Compressed air chamber made out of PVC pipe and generally mounted underneath or next to the barrel rather than in line with it.
This is pressurized through a snifter valve or something like that and either an air compressor or a bicycle pump, though, it takes quite a lot of pumping to pressurize them with a bike pump.
The real trick to building one is figuring out how to get all the air that you've pressurized into the barrel before the Spug leaves it.
The simple easy to build ones generally use like a ball valve which you turn yourself, but this only has moderate flow rate and it doesn't turn on that fast.
Another step up from that is using a sprinkler valve from an automatic sprinkler system.
These work by having a diaphragm placed sideways in the valve, which is put in such a way it has a small hole through it that pressurizes the section behind the diaphragm and keeps it not actually pushed by the pressure onto the mouth of the pressure pipe leading into it.
But it keeps it so that the pressure is the same on both sides so that the little bit of spring to the rubber keeps it shut and then normally a solenoid opens up and lets the pressure out from behind that diaphragm so the high pressure will blow the valve out of the way and go into the Spug gun.
But generally you want to modify this kind of valve with some sort of larger higher flow rate things so that it depressurizes instantly as soon as you hit whatever trigger you've rigged up.
When I've seen one of these it was hooked up with a cleaning attachment for air compressor cemented into the top of the valve.
The solenoid taken all the way out to hold drilled in the top of the valve and a cleaning head for air compressor equipped with a pop valve set up to release the air, which is actually a really nice setup because this kind of head already has a trigger on it.
So you have a trigger even though it's not mounted in the traditional firearms orientation.
So a sprinkler valve is a step up from the ball valve but still the air is going around 2 or 390 degree bends and so creates quite a bit of turbulence and it's not the highest flow rate valve but it's probably your best choice for building a basic one.
Now of course there's plans out there for air powered Spug guns so I'm not going to give you a whole another set of plans but this is definitely the next step up from a combustion powered Spug gun.
The advantages of air powered ones are you can do such things as having two pressure chambers where you have a large pressure chamber that you fill up as far as you dare and then a smaller one which you can fill for each shot out of that.
So that if you're using a port T-shirt launcher say you can do multiple shots without having to go back to the air compressor and you definitely want to use the air powered one for a T-shirt launcher.
You don't really want to shoot burning T-shirts into your audience and another advantage is that they don't get all gummed up from the actual product of hairspray and stuff.
They stay nice and clean because well air is pretty clean compared to hairspray and also they don't rely on a potato or something like that ceiling the end.
They still get pressurized even without a complete seal unlike combustion powered ones where if you don't hit if you have something that's kind of loose in the barrel all the gases will kind of flow out and around it and you can't really achieve anything useful with it.
So you can watch stuff that is smaller than your barrels and I've heard of people watching say golf balls long ways with these and all sorts of other interesting stuff so it really opens up your range of projectiles.
For starting out I would definitely recommend building either a combustion or airports but gun but if you want to go beyond that there are many different fields of experimentation.
One of the ones that I find kind of interesting is the hybrid spug gun.
In this you take and put a burstable membrane across the top of the combustion chamber in a combustion spug gun and then you mix up a ideal mixture of air and the fuel generally propane since that is easily metered and doesn't have the problems of hairspraying stuff like that.
You mix those up and you actually pressurize them so that when you fire it there is a lot more energy per cubic inch and so you can achieve higher muzzle velocities that way.
You can also build miniature spug guns which is a really good idea if you live in the city where you don't want to be breaking windows or knocking people's walls down and stuff and one of the resources that I'm going to list them which is going to be in the show notes gives the plans for building a tiny spug gun which is a little bit more difficult to operate but it's still fun and you can shoot little bits of potato all over the place.
Make a big mess with it. Another way to go is to make huge spug guns.
Another of the resources that I'm going to list Spudtech.com is the place that sells air cannons to FEMA for testing the tornado proofness of structures and they build this huge one that launches a 2x4 at over 100 miles an hour which yeah that's really crazy.
Also people have experimented with firing spug guns or firing spuds out of cannons with dry ice bombs which is another type of bursting valve.
This isn't really recommended because you can have hang fires and miss fires at rather in opportune moments but it's quite spectacular from the videos I've seen.
As I mentioned before you can step up your fuels to propane rather than the aerosols of spray cans.
This is more consistent easier to work with once you've got the tools and provides a little bit more bane.
Also you can build a breach loading spug gun which basically has in one design that I've seen has the barrel extend right through the firing chamber.
Come out the back of the gun just covered by a cap and have the potato knife on this one.
So you take the cap off, shove the potato onto the potato knife and then spray whatever you're using for fuel in and shut it up and you don't even have to set it down on its rear which is really nice.
It makes it a lot easier to use it and of course you don't have to have a calibrate a broomstick or whatever to make sure that you've got the potato at the right point.
Another thing that I saw on this design was a mixing fan inside the chamber which helps air out the chamber quicker after shots and make sure that all of the fuel is mixed together each shot which is really cool.
Now I've mentioned several times that I was going to give you some resources to find out more about this subject so here they are.
Most of these sites also include plans for building your guns and like I said I'd rather you got your plans from these than from this show.
So first one is Spudtech.com. I'm not going to spell them out because they're going to be in the show notes.
So Spudtech.com is about the biggest potato gun website on the internet.
The proprietors sells a whole bunch of different models of Spud guns from the $45 simulator which is actually a really incredible price.
That's its price at the time of recording. That's of course without shipping but I don't think you could find a better price anywhere.
Well actually the proprietor says that you can't find a better price anywhere that he's aware of.
That is also the shop that makes the $3,500 mega launch or two for testing buildings for tornado resistance.
The second site is SpudFiles.com. This is more of a forums type of site.
I haven't been around it much but it looks like there is a whole ton of information and cool pictures and videos of everything from some of automatic launchers to reviews of commercial launchers and all that sort of interesting stuff.
Then another one is advancedspuds.com which site includes a lot of different interesting articles about variables that you can change, different fuels that you can use, ignitions and something about theory of Spud guns.
So actually that's the kind of site that I really like to read. Also I mentioned the book which I was giving the plans from earlier on in the show.
These are the plans which I built my first Spud gun from and the book is Backyard Ballistics by William Gerstel, GUR STEL LE.
I hope that's pronounced right. Printed in 2001 by Chicago Review Press Incorporated.
This is actually a really cool book. William Gerstel has written several interesting books including another that I have building bots about building fighting robots.
Backyard Ballistics includes not only plans for Spud gun, combustion Spud gun contains plans for pneumatic Spud gun, match rockets.
You can actually make a miniature rocket out of paper matches and aluminum foil, hydro pump rockets, Cincinnati fire kite, miniature catapult, tennis ball mortar, all sorts of other interesting stuff.
So I highly recommend this book, especially since it has complete plans for all of the stuff which it discusses.
Now I guess you could take this either as like cautionary or amusing, but I decided I'd close out the show with a couple of stories which were posted up on Spudtech.com.
Yeah, definitely cautionary, I find it funny. Most of them probably funny after the fact which is the way a lot of this stuff is.
First one is by a guy who calls himself Papa Smurf. He writes, oh yeah I have a story to tell you and maybe you can put this on your site to warn people not to make the same mistake I did.
When constructing my first gun I couldn't get enough spark from the barbecue igniter to light the fuel. I did as recommended, spray for one to two seconds.
When I opened the back of the chamber to let air, it air out while I rewired my barbecue igniter.
While I was doing this I still had a Spud in the barrel and the butt of the gun was pointing up. About ten minutes had gone by, I put the barbecue igniter back on the gun.
Now I figured that since I left the back of the gun open for about ten minutes that all the fuel would have been gone.
While I was wrong because when I put the barbecue igniter on it looked down inside to see if it would spark and I hit the button.
Boom! I was very lucky not to have gotten seriously injured.
My eyebrows and eyelashes were total lost and my bangs are extremely short now and I had some burns on my nose and under my eyes and forehead.
The lesson here is to never think that all the fuel is gone from your gun even if it doesn't fire and that doesn't mean that it's empty.
It could simply mean that there isn't enough oxygen to fuel ratio in the chamber.
I guess what happened to me is that since the potato was still in the barrel and that hair spray is a heavy gas it all settled to the bottom and when I hit the button, boom!
So I have now learned a good lesson. Never looked down the barrel or the rear opening of the gun. Another good idea would be to have some parental supervision as well.
I was by myself and didn't know what I was doing. Yeah, I think those are all really good ideas.
Another one was submitted by an anonymous user. It goes a couple of years ago when I was seventeen my brother and I decided to make a potato cannon.
Nah, I'm betting a little bit about regional dialect here. We used a four inch by three foot combustion chamber and a three inch by eight foot barrel that was interchangeable with smaller barrels, but they're less fun.
For ignition, we used a flint igniter for Coleman lanterns because they're only three dollars compared to fifteen for a piezoelectric grill igniter.
Unfortunately, we could not find any potatoes that were large enough to launch so we bought a few rutabagas instead. They would wait in at about three pounds apiece.
On our first launch ever, we filled the chamber with eight seconds of Aussie hair spray. Believe it or not, that's actually the optimum amount. We figured that out later through trial and error.
Hit the igniter and sent the rutabagas so far over the lake that we were at that we couldn't see where it landed.
An over-later, one of my cousins got back on his jet ski and said that he had just helped the dude out of a sinking robot.
The roar set a flying vegetable. He didn't know it was a rutabagas had blown a hole in the bottom of his boat. Now that was close.
There's more to this story, however. Later that day, we figured out how to launch popcans using newspaper as a plug to seal the barrel.
We decided using our knowledge as physics to calculate the muzzle velocity by timing the amount of time the cam was in the air.
After filling the popcam with water, we launched it straight up, a little over eight seconds later it landed on a decorative stone about a foot away from me, shattering the stone.
We later calculated the velocity to be about 33 meters per second or 75 miles per hour. That was one sweet cannon.
And I'll have to say that guy got really lucky twice in one day.
If you like these stories, there's lots more like them on Spudtech.com under Stories. And if you are now interested in Spud guns, I highly recommend building one.
So, this has been another informational and exciting episode of Patrick Public Radio.
Thank you for listening to Patrick Public Radio.
The SPR is sponsored by Carol.net, so head on over to C-A-R-O dot N-E-C for all of her TV.
Thank you very much.