3D Printed Spuds Are Begging To Be Fired

The ballistics of humble potato is a time-honoured research topic for everyone who likes things that go bang. The focus of such work is usually on the launcher itself, with the projectiles being little more than an afterthought. [drenehtsral] decided that the wares of the local organic ammunition supplier were not good enough for him and his minions, so he designed and then 3D printed some rifled potato cannon slugs.

The design was done using OpenSCAD, has a number of adjustable parameters like infill and rifling. We doubt that the rifling introduces any spin, since it is being fired from a smooth bore barrel, but as always 3D printing brings the capability to quickly test different ideas. A quick search on Thingiverse shows a number of 3D printed spuds, so [drenehtsral] is not the first give it a go. However, this did bring to our attention that the field of spud gun projectiles is begging to be explored.

There is enough space inside a projectile to fit an IMU and logging electronics, which would give some very nice empirical data (providing you can recover it of course) on spin, acceleration, and trajectory that can be used to further improve designs. Spring loaded stabilising fins would be cool, and maybe someone can even manage to implement some form of guidance? The possibilities are endless! If you’re up for the challenge, please document your work it and let us know.

As you would expect we have no shortage of potato cannon themed content, ranging from cartridge firing and bolt action versions to antenna launchers and Arduino-powered fire control systems.

52 thoughts on “3D Printed Spuds Are Begging To Be Fired

  1. It’s not clear to me that you’d want a spud to spin. Unless you’re careful to carve out just a select core section, the mass won’t be uniformly distributed about the spin axis. Unbalanced spin would introduce wobble and thus reduce aerodynamic performance. Most spuds I’ve launched did pretty well in this regard, w/o any spin.

      1. Gunpowder by itself I don’t think would do much other than scare people since you need something to ignite and set off the gunpowder. Just sort of like you can drop a can of gunpowder and all it does is scare you unless there is a spark.

          1. djsmiley2k – RDX is indeed poisonous, but does not dissolve well in water, so it’s difficult to get any meaningful dose into your body
            No idea about the plasticizer.

          2. IIRC – According to my USAF Munitions Systems training almost 20 years ago chewing it produces psychoactive effects, so a bittering agent was added to make it less tempting.
            That MAY be an urban legend as the instructors didn’t provide any evidence to back up the claims.

      2. Funny you should mention that, my son was lobbying for me to try casting one in aluminum and I had to explain that we didn’t have a sturdy enough backstop to safely launch such a projectile given how the plain old garden variety (har har) potato he’d just fired punched a deep dent in the weathered slab of 3/4″ MDF we had been using as a backstop. I have a feeling he’s going to be as unruly a teenager as I once was…

          1. In my extensive testing I’ve found the following are pretty formidable projectiles:

            *Kumara (sweet potato). More fibrous so less likely to shatter than a regular potato.
            *Onions – create a great seal. Suspect the layers of skins also help prevent shattering.
            *Lemons and Limes. The greener the tougher.
            *Water balloons. Grab a few, stick the first one over a pencil (eraser end) then keep layering. 3 layers seems to be pretty safe. Fill them till they’re roughly golf ball sized. Great seal. The first layer or two gets stripped away on launch but the remaining little ballon keeps flying. packs a hell of a punch :-) Only ever tried it out of a pneumatic cannon – suspect flames might kill them though.
            *Golf balls. Sent one right through the door skin of a burnt out car once….

  2. Clearly an idea that bears merit enough to test out, but untried until now. If you look at the normal spud gun’s projectile in flight it is already typically spinning along some random axis, so why not try to add some control to that! Well may give an accuracy boost.

    Definite thumbs up for the experiment. I like! Good hack. Whether it worked or not is almost moot as the experience and knowledge gained is the point. Better yet because passed the knowledge on.

  3. Just throwing this out there as most people don’t realize. A combustion powered potato cannon is considered a firearm in many USA jurisdictions and one with a bore larger than 0.5″ is classified as a destructive device in the USA. That means to manufacture and possess one you are required to have a $200 NFA tax stamp from the ATF.

    1. You raise a valid point and it’s very important to follow all applicable laws, but a bore larger than .50 makes it an Any Other Weapon (AOW) not a destructive device under federal law. Please do your own research and do not trust me on this.

      It is legal to manufacture firearms for one’s own possession in most U.S. jurisdictions. As long as one follows the laws.

      1. I have US Code if that works.

        18 U.S. Code § 921(A) 3: “The term “firearm” means (A) any weapon (including a starter gun) which will or is designed to or may readily be converted to expel a projectile by the action of an explosive”

        26 U.S.C. § 5845(F): The term “destructive device” means […](2) any type of weapon by whatever name known which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant, the barrel or barrels of which have a bore of more than one-half inch in diameter, except a shotgun or shotgun shell which the Secretary finds is generally recognized as particularly suitable for sporting purposes; […]

    2. No it’s not.
      The BATFE has commented on this many times. Potato guns are not considered firearms, destructive devices, or any other contrivance under their jurisdiction.
      That said, if you use them irresponsibly expect criminal charges. And as always check your local laws, I’m not a lawyer, and that wasn’t me giving you legal advice. If you end up in jail, it’s your own fault.

      1. Please provide citing. US code sure sounds clear. Just because the BATF says something doesn’t make it true and also doesn’t mean they can’t change their opinion on a whim or a request from the president as they did with defining bumpstocks (an accessory) as a firearm on its own and machine gun… I choose to keep my firearm rights and NFA items and avoid a felony.

        1. Actually the BATFE saying something, being the regulatory agency DOES make it true. Remember these are the folks who said back in the 1990s that a shoestring is a firearm, specifically a machinegun. They later revised that to “a shoestring under certain circumstances” is a firearm, specifically a machinegun. Fun fact: Every explosion and every squib simulating being hit by a gunshot in a movie is a Destructive Device and must be paid for.

          It’s important to do one’s research and not break the law.

        2. I did provide a citing, if you can be bothered to combine “batfe comment potato cannon” with your favorite search engine, I can’t help you.

          On their FAQs you’ll find the context they consider when deciding if your novelty starch accelerator is actually a regulated device.
          Muzzle loaders (most potato canon) are exempt from the 0.5″ rule as evident by every modern muzzle loader, black powder canon and mortars. Again, don’t use spudguns to destroy other people’s stuff or wake the neighbors up and no one cares. If you’re really nervous, stick to compressed air.

    1. I like that idea ! Or you could just mash the potato and stuff it into the sabot. But I have to believe that at some point creating plastic containers and filling them with “stuff” and adding guidance will run afoul of some local law authorities, if not the BATF. I wouldn’t advertise my success on Youtube.

      All of this is beginning to sound like a lot of work.

      1. Just having it use combustion will classify it as a firearm and bore size(over .5”) could end up classifying it as a destructive device requiring a tax stamp or risk of a felony and 10 years in prison for violating the NFA. No different that possessing an unregistered short barreled shotgun/rifle or suppressor.

        1. IIRC the BATF says they are legal but I’m not going to press that issue with the Feds. they aren’t likely to bother you unless you do something monumentally idiot. OTOH the local LEOs may have other laws and opinions. Again don’t be a jerk and the worst you’d likely get is a “Gibbs smack”. I’d be more cautious in the PRM and/or NY and/or CA and/or NJ.

      1. Yes, though we had a separate section of “barrel tube”, ground as you describe above. It was clamped in a WorkMate and we pounded/pushed spuds through it with a 2×4 and stick so as to have a ready supply of pre-cored potatoes on hand.

      2. A few points, I prefer pneumatic cannons because they are less hassle and no combustion. I filed the end of my barrel to allow easy shaping and loading with a broom handle to push the payload in. The rifling on the slug above looks too extreme, I think it is supposed to only be a half twist or less for a regular rifle over the length of the barrel so it doesn’t take much to stabilize the projectile. In high school in the 90s my physics teacher brought in his potato gun with a 2″ barrel and we loaded it with water filled 20 oz soda bottles. We experimented with rifling, find, nose cones, etc. Nothing really made a difference though.

    2. A while back some guy was selling rifled sch80 pvc. He even took the time to get twist rates slow enough so your tuber wouldn’t disintegrate. Shouldn’t be that hard to make a broach and replicate the effect.

    3. Just make the inverse of that shape, and fit it around your potatoes when they’re still very small. As they grow, they’ll be forced into the desired shape…maybe.
      It works ok with fruit like tomatoes, I have no idea if it’ll work for a spud.

      1. I don’t think it would. Potatoes grow on the root, underground, not on the vine where it’s easy to see and get to them with a forming box. But melons… now you have something on a vine and with enough mass and density to go deer hunting.

  4. I can confirm that a small NERF football is awesome ammunition. It needs a little oil to make it slippery, but perfectly seals and is highly repeatable and almost never misfires. Plus, it flies way farther and straighter than any vegetable I’ve ever tried. and whistles! The kind I’ve used has a whistle and a small tail to keep it straight, I bought them on amazon for about $6 each.

    1. Thx for that. I’ve been interested in getting pool (billiards) spin and trajectory data using an RPi and had considered a strobe method to do it. I’m not sure I can get a balanced exposure given I can’t very well shoot in the dark but some sort of ND filter combined with a strong strobe … ??

      1. I don’t come from photography and did not know about ND filters. But probably you don’t need them.
        Billard ball is relatively slow compared to pellet shots (at most 16m/s from https://billiards.colostate.edu/faq/speed/typical/). Diameter of amarican ball is 57mm, so time between exposures needs to be >0.057/16 for fastest shots and even bigger for slower shots in order to get non-overlapping exposures. Lets take 0.004s as extreme. Taking 2MP video with Raspberry v1 camera at 30fps will have (1/0.004)/30<9 exposures per frame. So you can just do PWM exposure with 250Hz, and images will not be too bright with say 9µs flash durations (example with five 9µs flashes here: https://raw.githubusercontent.com/Hermann-SW/Raspberry_v1_camera_global_external_shutter/master/res/audio_shots.c.5_9_6000_2000.png). You will need to put some marker on billard ball like I did with blue dot on pellet (should not be a problem given billard ball is "heavy"). You will need several 5000lm leds with 1.5W led driver and reflector ($12 per triple) to light the whole area. No shoot in dark necessary, I have computer monitor 1.5m distant from scene on (not direction of scene), that allows humans to see enough. You can take a low light to light the scene allowing you to shoot well, it just needs to result in dark 30fps frames without flashes.

  5. I’ve built a couple of pneumatic cannons now, ranging from small to “We should get a boat to mount this on”. As kids, we had one bad experience with a potato gun, and witnessed two others, so I’m avoiding combustible PVC spud guns.
    The latest was a large cannon (2″ bore, probably a 1.5 to 2 meter barrel, and about a half a meter pressure cylinder) and mount (from a surplus office rolley chair), for the 4th of July. I made a fun little “Det Box” to actuate the sprinkler valve, complete with key lock, safety, warning buzzer, and power display. The idea was to make the firing sequence as interactive as possible.
    We 3D printed a dozen or so projectiles using OnShape (Much more of the finned Nerf variety than the solid slug), and finished all of this the afternoon of 4th of July.
    We packed everything out, headed to the family farm, and folks went a little nuts. The kids loved it (Push a button, shoot a cannon… Yeah, I get that), and it was pretty cool watching them get the safety sequence down (no one near the cannon while the warning buzzer was going. Always call out “Clear!” and get the fire order from the firing officer (mom or dad)).

    With hollow projectiles we were getting a good 200+ meters out of it. The kids would fire off the projectiles, trying to figure out which one would fly the best, then spend a good 20 minutes in the fields bringing them back.

    We didn’t try any backstop tests… But previously we did have a very small compression launcher that could take a squash ball in a 1.5″ barrel… We called it the Squash Ball of Inevitable Lawsuit. We shot it at a riot shield wielding team mate, and he stated “That was not fun, let’s not do that again”. Not very scientific, but fun times.

  6. My neighbor and I when we were young used to build all sorts of potato guns. We’d experiment with shooting basically anything we could find that would fit in the barrel. One of our favorites was to raid his dad’s box of shotgun shells left over from pheasant hunting (he would buy a new box every time he’d go out, and any remaining shells he’d dump in a box in the basement). We’d carefully saw apart the shells through the wad and empty out the gunpowder for use in various nefarious explosive devices. We would then VERY carefully cut out the primer from the brass base of the shell, Fill a dixie cup with 10-20 bare primers and load it down the barrel. When shot at a hard surface it’d make quite a racket, and if you fired it straight up it would rain back down and the primers would explode when they hit the ground.

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