The Spud Gun To End All Spud Guns

In Norse mythology, Mjöllnir is the hammer of Thor, forged in a contest to create the most wondrous and munificent tool for the gods of Asgard. While we’re not aware if [MrCrowley] recently made a bet with Loki, his version of Mjöllnir, a gigantic spud gun powered by MAPP gas, is wondrous enough for our tastes.

Unlike most of the other spud guns we’ve seen, [MrCrowley] eschewed the use of PVC pipe and fittings in his build because that would explode on the first test fire. Instead, the gun uses galvanized and stainless steel for the majority of the construction. That’s not to say this spud gun is necessarily safe, though: as he demonstrates in the video after the break, golf balls exit the barrel with a comparable energy to most rifle rounds.

For an interesting take on an ignition system, [MrCrowley] built a remote ignition system out of a wireless doorbell and a 100kV stun gun. While this does allow for remote firing, the entire build seems safe enough – from behind the muzzle, at least – to be carried with a rifle strap.

It should go without saying that this is incredibly dangerous and you shouldn’t build this if you’re not planning on your last words being, “Wanna see something cool? Hold my beer.” That being said, [MrCrowley] knows what he’s doing, and you can check out the video of Mjöllnir in action after the break.



74 thoughts on “The Spud Gun To End All Spud Guns

    1. Ay true, but I think it would be hard to make a simple system to improve accuracy as its a smooth bore barrel with waded projectiles (mostly) and/or round projectiles. I will admit that I am mightily impressed with the range and power of the thing!

      1. bah, nothing a simple sabot can’t fix… just have the sabot impart some rotation to the projectile before it separates or cut a few rudimentary fins into the spud and use a sabot. once the sabot separates, the airflow over the spud should impart some stabilizing rotation onto the spud.

        such as these:–9LElYNcUFHMeMVu8A

      2. This gun will be inherently inaccurate due to barrel harmonics. If you look at the part of the video where the cannon is on the ground firing w/o a projectile, you can see the barrel bounce around, even before it was fired.

      3. Thanks for the comments Big_James.

        I’m not too concerned with accuracy as it wasn’t really a goal I was trying to achieve with making this cannon. Generally, If I’m aiming at something I want the most power available to try and destroy it, so naturally I’ll shoot from as close as I can without risking injury. I can hit a 1′ x 1′ object at about 30′ without too much problem.

        I think if I were to try and shoot something from a small distance, like 100′ or so, I would be aiming at something large enough that I could reliably hit from that range; like a car sized target. Golf balls are tricky though, they’re not very accurate and like to hook or spilce a lot.


      4. Blue Footed Booby – yes, the m1a1/a2 were all upgraded in 1990 to the M256 smoothbore gun, but we’re all rifled before that. Since being updated, they all use M829A3 standard Armour piercing rounds and M830A1 HEAT MP-T rounds, and they are both fun stabilized Sabot rounds (armour-piercing fin-stabilized discarding sabot (APFSDS))
        All was searched on wikipedia. Just reinforcing my sabot idea…lol

    1. “Terrorist”? Sure, throw that stupid, overused label on everything you’re opposed to or are afraid of. He’s just a kid who’s experimenting with something fun. Quit looking for some bogeyman under your bed and lighten up.

      1. I see you randomly firing a high velocity weapon over farmland. No concern for whomever might be down range. That goes against everything that I have been taught about gun safety. You don’t have to be a terrorist to harm or kill some innocent person

        1. Well… While safety is some thing everyone should be educated on, you kind of put it in perspective yourself.. he is firing over farmland, which I would suspect has pretty good line of sight on anyone that would be there

      2. You sir, as well as the incredibly (I’m assuming self taught,) strong minded engineer of this truly awesome piece of recreational dream fodder… Are just the type of folks I hope to meet, befriend, and collaborate with someday. I live in San Francisco. Where everyone is afraid of everything! Surprisingly enough the police here enjoy my projects more so than anyone. Thanks for giving that douche a little perspective ;)

    2. You know what would make an ideal weapon for terrorists ?

      a quadrocopter or an FPV RC plane… just put 0.25kg of C4 on it and you’ve got a cruise missile for mere 600$

    3. You could kill someone with a nice rock, that’s why when I run for office my tough on crime campaign will seek to outlaw unregistered rock owners. Think about the Children…. Yawn.

  1. There is nothing safe about this. ‘Eschewing PVC’ in favor of metal is not wise, as all this means is the pressures it develops will be that much higher, and the shrapnel from a catastrophic failure is that much more dangerous.

    All in all something you should NOT do unless you are a trained, certified gunsmith. I think the government would agree.

    1. There’s not really such a thing a certified gunsmiths. There are schools that teach it and they give some sort of degrees but most gunsmiths are usually self taught or learned from another smith.

    2. The government would not agree. To build firearms all you need is a license, not schooling or certification (not that there is any real certification). Also the ATF would probably frown upon this since it would probably fall under the definition of a NFA regulated destructive device.

  2. So is it a one shot kinda thing then?
    If not I would love to see it have a magazine of ammo would make it a formidable DiY weapon instead of just a toy, comparable to a muzzle loader.

    1. not hardly, you coult put a t on the barrel facing up and a valve bigger tha n your ammo and open the valve to drop one more shot, then fire then another.

    1. Hey is this the same FiveseveN that used to frequent Spudfiles?

      It indeed is not the biggest, nor most powerful, however it shares the title of the most powerful handheld cannon (not including black powder cannons, of course) along with someone else from Spudfiles who has a cannon similar to this one. And this is one of maybe three or four piston valved hybrids; so while not necessarily innovative it wasn’t exactly a standard design to make.

      There’s a relatively new 2″ burst disk hybrid, by mobile chernobyl, over at Spudfiles that would definitely be more powerful than this; it’s mounted on a small trailer too.

  3. Just wanted to point out that metal pressurized mapp/propane/etc powered combustion guns have been rather commonplace in the spudgun hobby world for the last several years. Stun gun ignition has also been the preferred ignition source for combustion cannons for at least ~10 years. Not meaning to knock the build but i have seen far more impressive cannons when i used to be reallyinto the hobby 8 years ago.

    1. Hi thanks for the comment, Nick.

      Yes, stungun ignition and MAPP guns are quite common these days but 10x mix hybrid propane/MAPP cannons aren’t really all that common; especially with large chamber volumes like this. But you’re right, I would agree that hybrids aren’t anything new these days but the most unique thing about this cannon is the pilot-vented piston valve (instead of burst disk on most cannons); this being only one of two or three, to my knowledge.


  4. ROFL report him to Homeland Security. I can see it now:

    “Yes I’d like to report a terroristz!!”
    “What’s the issue sir?”
    “He’s gotz hugez spudz gunz and I’s scardez!!”

  5. I have a hard time believing this thing is putting out golf balls with as much energy as a rifle round, unless your talking 22 Short. What is the weight and velocity of the golf balls, and how far away is the chronograph from the muzzle? .308 will easily give 2600 ft/lbs of energy, even a small rifle round like 5.56 NATO will give 1700 ft/lbs.

    1. So it looks like he didnt actually figure out the velocity of the rounds, he used a crude calculator to guess, which is going to be very far off. In the gun world, the only internal ballistics software I know of is QuickLOAD which is covered in warnings about how it will be off by at least 10%. With something like a DIY cannon your going to be off by a lot more, especially so due to the comparatively crude construction methods and tolerances. That doesnt take in to account that the golf ball is going to be losing far more energy that a proper bullet would.

      1. He didnt use a real chronograph. He used a microphone and then later on attempted to make a DIY one without validating it worked. He also placed the phototransistor one far too close to the muzzle. The muzzle blast can be registered by the “chrono” and will give bad results, this is in the manual for any chrono intended to be used with a firearm. Its not like firearm chronos are that expensive, they can be had for ~$100 new and even less used.

        In addition he never recorded a velocity anywhere close to what he claimed with his “internal ballistics” software. The most in that chrony video was 173 m/sec compared to 519 m/sec in video with the software.

    2. Hi Matt, thanks for the comment.

      I used HGDT to calculate the results, which is accurate to about 10% +-, perhaps slightly less at supersonic velocities. I myself don’t believe I am getting golf balls to shoot 600-500 meters per second at 10x mix, 450ms is probably a closer and much more realistic figure, which is still 3000ft/lbs. The reason I haven’t chrony’d this with my F1 chrony is because I use a sabot for the golf balls and if I shoot from a distance where the sabot wont interfere, the golf balls might hook or slice and miss the chrony. I’ve used frame rate measurements of the video and got transonic golf ball velocities over a distance of 60m or so; which means muzzle velocity is probably up near

      “The most in that chrony video was 173 m/sec compared to 519 m/sec in video with the software.”

      You must be mistaken as I’ve never attempted to chrony this cannon with my PT chrony before. I’ve only chrony’d a pneumatic cannon made of PVC shooting golf balls.

      I would like to mention that this software is designed by “David Hall. I’m a Mechanical Engineer employed at the Naval Air Warfare Center, Weapons Division, Ordnance Test & Evaluation Branch. I started my career writing flight simulations. These days I test bombs, rockets, and guns.”, so it’s not exactly a basic calculator but it’s not 100% accurate, like I said we take the results to be relatively accurate.

      That being said, firing a heavy enough projectile (160g or so) and I can push the muzzle energy up near 8000ft/lbs, and that’s taking in to account a 11% error in calculations.

      I appreciate your comments, Matt, and I can understand your apprehension about accepting the results but I thought I’d just comment and clear a few things up. I wish it were as simple as firing a golf ball over my F1 Chrony but it’s proved too difficult so far.

      P.S. I have chrony’d a much smaller hybrid and got readings of over 1400fps from a 3/4″ barrel and 10mm ball bearing with a sabot. I think it’s possible that I could even push that up to 1600fps with a better sabot.

    3. Matt,

      Being an armchair engineer might earn you some credit on a forum, but do some more research before making conclusive statements about something you’ve just seen for the first time today.

      He is easily exceeding the kinetic energy of that of a .22 round.

      Here is a creation of mine using very similar tech that can reach velocities close to that of a .22 round, but packing well over 5000 ft-lbf.

      And another design very similar to the one posted here:–Iw_8td5-oC4uPUg1A&index=1&feature=plpp_video

      The reason our creations are high in KE is not due to velocity, but rather the weight of the projectile. Most of these guns are under 2000 fps in velocity. That is except for this one:

  6. He had better be careful when he mixes the gases. It will get dangerous when the partial pressure of oxygen becomes 100 percent at normal atmosphere in the chamber. Someone (Coroner) may be picking up pieces of him off the ground….

  7. When life gives you lemons, don’t make lemonade. Make life take the lemons back! GET MAD! I DON’T WANT YOUR DAMN LEMONS! WHAT AM I SUPPOSED TO DO WITH THESE!? Demand to see life’s manager! Freeze the lemons, then when the manager comes back SHOOT HIM IN THE FACE WITH THIS MAPP CANNON! DO YOU KNOW WHO I AM!? I’M THE MAN WHO’S GOING TO SHOOT YOU IN THE FACE WITH FROZEN LEMONS!!

  8. Crap article… Doesn’t even mention the fact that this gun is a PISTON HYBRID. No burst disc, and hardly a “simple potato tosser”. It’s easily one of the most powerful handheld hybrids out there, and he can reload it in seconds, rather than the minutes needed for most hybrids.

    As for legality, the ATF has SPECIFICALLY declined jurisdiction on recreational launchers constructed with plumbing fittings, and using either air pressure or explosive gas. The only circumstances under which they would ever classify this as a destructive device is if it were to be used in a NON-recreational manner, such as hunting or being used in the commission of a crime.

  9. Ahh the good old spud gun, this takes me back to my first arrest.
    Dont build one of these if you live in NSW Australia, The cops don’t like getting in their tactical gear when some dumbs neighbour reports that you’re shooting a “rocket launcher” blocks the streets off and send seven guys with the kevlar vests and helmets to surround the property and arrest you only to find out it was a potato cannon. Take it from me.

  10. An awesome display of backyard “engineering”. Sure, one could get hurt by it’s use or misuse, but then… “Stupid is SUPPOSED to hurt”. It does look like he used schedule 80 pvc for the barrel. Pretty heavy walled stuff. I can’t believe all the pussies complaining about “terrorism and so forth. We made tennis ball cannons with gasoline and lit them with matches. Worked AWESOME! Smart? No. Safe? Not even close. Must have made 2 dozen. Beyond “Lucky”. One can make incredibly dangerous stuff, but guided by common sense, 3x remote testing, you can get away with quite alot. Bomb making on the otherhand, isn’t stupid, that goes clear over to the Darwinian. Some folks never get a chance to pee in the gene pool…

    1. Thanks for the comment, Burnerjack. The original barrel was actually PN15 6mm wall ABS. Although only rated for a few hundred PSI, ABS pipe tests by others had shown that it was capable of taking the momentary pressure. It also has excellent fail characteristics as it splits or tears rather than shrapenls. I’ve had a copper barrel explode before (video on my PerformanceCannons channel) and it tore rather than shrapnelled, testament to its failure characteristics.

      As seen from the photo in this article, I have replaced the ABS barrel with S/S pipe with a yield of several thousand PSI, I believe.


      1. You are talking about the black plastic (abs) piping right…? Do they really have pressure ratings hight than that of just sch 40 pvc? I’m c currently using PVC for my pneumatic standard old everyday airgun trigger modified sprinkler valve rig, but I used to use that black ABS piping when I first started many many years ago working with hairspray and what have you, but I started to notice myself as well as herd that abs for combustion is no good because it deteriorates faster.. so I mean which one would be best overall for a hybrid Cannon if I wanted to build one, I think it’s been a long time coming thank you!

    1. Hi Brad,

      The turntable was kaput, so it was put out of its misery. Of course, I only did this because I have a Akai turntable in my room with a perfectly good needle and the automatic arm is still in working order! My small LP collection may not be to everyone’s taste but it surely has some good music in it ;)

  11. The whole purpose of a high powered weapon is so you don’t have to be close up to whatever you are trying to hit. Otherwise you could just carry a club & skip all the engineering.

    1. I appreciate the comment Micky, I’m not sure if it was a dig at my practice of shooting targets at relatively close range but the purpose of this cannon was not so I could fire from a long distance. Rather, it was so I could shoot long distance or achieve a great deal of muzzle energy from a relatively small cannon.


  12. It is good to know that you can get a remote ignition system for an air cannon. That does seem like it could make using one an even safer. My brother would totally love to get a spud gun like this. I wonder what else you could use the cannon for.

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