The Miniature Bolt-Action Pneumatic Potato Gun – Part 1: The bolt

I don’t recommend trying this and can’t guarantee that it’s safe.  PVC pipe is generally not rated for holding air pressure.

Years ago, I made a cannon that shot grapes, tater-tots, or cut potatoes with a 1/2 inch length of PVC pipe.  The innovative part of this was that it used a bolt-action mechanism to open and close the breech.  This meant that instead of having to stuff the projectile down the muzzle of the “gun” into the “chamber”, it could simply be placed in the breech and closed.  Bolt-action rifles were, of course, invented long ago, so I can’t take the credit for this.  One that fired potatoes would not come until much later though.

Here is what I came up with:

full bolt action mini potato cannon

I go over the pneumatics in this post, but here’s an animation of the bolt mechanism and how it works:

bolt action potato gun mechanism

The chamber is opened with, literally, a bolt.  In this case, a 1/4 – 20 bolt.  When the chamber is opened, one can put a pre-cut potato or other projectile into it, close the bolt, and then blow air down the chamber with the valve of your choice (more on this later).  The outer (1 inch) piece of pipe is cut out to guide the bolt down into the barrel.  The cutout then turns to the right, locking everything in place.

cutout to guide bolt

PVC cutout for bolt


The actual sliding bolt mechanism was made from a piece of Delrin, which is a type of plastic with a very high resistance to abrasion and fairly low friction.  It was also what was available to me at the time.  There is a hole down the middle of it which allows air to pass through when fired.  One end is tapped for 1/4 inch NPT to allow a 1/4 inch air fitting to be screwed in.  The other end is cut just smaller than the inside diameter of the 1/2 inch pipe that it will be putting air into.  To keep air from escaping when fired, a slot is cut for an o-ring to provide for a tight seal.  Additionally, a 1/4 – 20 hole is tapped through one side to screw the bolt into.

internal part of the bolt-action grape gun

The sliding bolt by itself

Shown above is the sliding part of the bolt.  The “chamber”, shown to the right, is made out of a 1″ piece of PVC pipe.  Inside of this, another piece of Delrin is  cut on a lathe so the outside is a tight press fit on the inside of the 1″ pipe.  The middle of this Delrin spacer is drilled out so  that the 1/2 inch PVC barrel can be press fit into the assembly.pneumatic bolt illustration Additionally, the spacer and 1/2 inch PVC pipe facing inside is cut at 45 degrees to allow the projectile to slide into position.

The cutout illustration to the right should illustrate how everything fits together – even if the scale is off a bit.

Once everything is in place and sealed, air is sent down the barrel, sending the projectile down range.  Hopefully this post explains pretty well how the bolt and barrel works, in the next post I explain the pneumatics that allow this gun to get more than one shot per air fill.


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26 Comments.

  1. Bolt Action Pneumatic Spud Gun - Hack a Day - pingback on April 9, 2011 at 11:13 am
  2. Ok,So, where’s the target? hahah, you could of being charged for a homicide for shooting at passing by vehicle.

    • Haha, well it’s not the busiest street in the world… Plus, I think I could throw the potato harder to be honest. I do love Dr Pepper though, not that it has anything to do with anything.

  3. Haha, I made oe of these when i was in high school! Think bolt action that will load a whole potato with over 100psi of air behind it :)
    My sugestion, use a water sprinkler solenoid as the trigger…remote electronic trigger! yeah baby!

    Nice work!

    • Thanks! I’ve tried sprinkler solenoids for different projects in the past – had good results!

      The thing you made sounds like a pretty cool design! I’d love to see some pics!

  4. For me the pneumatics are the interesting part. What is that brass thing connecting the 2 chambers. It looks to me your using a high presser high volume tank. That connected to a fireing chamber. Are you using a slow leek, or is that just a press valve, or a regulator?

    • I agree, that is pretty interesting. I’m working on a post right now that should explain the pneumatics, so be sure to check back in a couple days. The brass thing is called a flow control, which is more or less just a way to have a controlled slow leak. They’re used in industrial pneumatics a lot to control the speed of pneumatic cylinders without necessarily impacting the force when fully extended.

  5. I tried a bolt action design similar to this several years ago, but I had problems with loosing pressure during firing. Do you loose very much though the bolt assembly?

  6. Great idea! Plan on doing this with my friends sometime this week, except on a much larger scale. Want it to go 100-150 feet. Same design would work I believe, with some minor modifications of course. Bigger tanks, larger barrel, etc. any idea on where to get the special valves needed? (I live in Canada lol)

    Great idea though!

    • Glad you liked it! I’ve used sprinkler valves for a larger pneumatic project, they seem to be pretty popular for this type of thing. I’ve used a manual water valve too, but I think you loose some of the force during the time it takes to open it.

      All that being said, be careful, especially if you’re going to scale this up – PVC isn’t generally rated for air pressure. I’ve heard some discussion about taping the wall with duct tape or encasing it in some sort of loose heavy cloth bag, but I’m not sure if that would help or not.

  7. This is an awesome build! I made a similar contraption but it was instead intended to be a nerf sniper rifle for a game of assassins at school. One of the various kinds of nerf darts fits perfectly into 1/2″ pvc pipe. I really like your idea of feeding the air directly into the bolt- my bolt action was more of a hollow tube that pushed the dart forward and blocked the breech to fire.

    I’m curious where you get plastic like the variety your mentioned. I had trouble finding anything like that. Great Job!

    • Thanks for the kind words! That’s interesting about feeding the air into a fixed breech position. That would make for much better air line management… Oddly enough I never thought to do it that way!

      I’m not sure where to get Delrin. I made this several years ago and I had some extra material available at work. As for plastics in general (Maybe Delrin too), I’ve used this supplier before: http://freckleface.com/shopsite_sc/store/html/plasticmaterial.html – they have pretty reasonable prices generally. If you can’t find what you’re looking for, try mcmastercarr.com – they have just about everything (probably Delrin now that I think about it), but they can be expensive.

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