How to Make an EASY SEMI-AUTO Spud Gun Out of a Fire Extinguisher Plus RIFLING

Introduction: How to Make an EASY SEMI-AUTO Spud Gun Out of a Fire Extinguisher Plus RIFLING

About: I like the great outdoors, I play video games, and I have a knack for building stuff.

This Instructable will show you how to make an air cannon out of a fire extinguisher and PVC and how to make a rifled barrel without any complicated machinery. By the end of this Instructable, you will learn how to make a spud gun that can hold ≤200 psi without any leaks and is semi-auto with full-auto capabilities. You will also learn how to make a very easy rifled barrel that can shoot .45 sabots accurately, or you can change to a smooth bore barrel to fire anything you want (potatoes, paintballs, darts, and let's not forget the shotgun shells we'll learn to make as well). Did I forget to mention that this project costed me a few cents? Now let's begin!

Disclaimer: Be safe with this air cannon as it is pretty powerful. Do fill it at above 200 psi even if your air compressor can do more.

Step 1: Materials

Here is the list of materials:

  • 1/2" PVC pipe
  • 3/4" PVC pipe
  • PVC glue and primer
  • Two 3/4" PVC end caps
  • One 3/4" PVC female threaded adapter
  • Two 3/4" PVC male threaded adapters
  • One 3/4" - 1/2" PVC reducer
  • One Schrader valve
  • Fire extinguisher (any dry chemical extinguisher will work, and it's preferable if your fire extinguisher is used)
  • Duct tape
  • .45 muzzle loader ammo with .50 sabots (hollow point rounds are a blast)
  • Cardboard or some spent .410 casings with wads
  • BB's or shot
  • Wire
  • Drill with a 1/2" drill bit and a smaller one (a Dremel might come in handy)
  • Epoxy
  • PVC glue
  • A thin dowel several feet long or something similar
  • Hacksaw
  • A good pair of scissors
  • Air compressor (preferably capable of 200 psi)
  • Paper towel

Step 2: How It Works

Before we get into the details of how to make this air cannon, let's understand how this gun works. Refer to the diagrams above.

The reason why we have to use 3/4" pipe for the base and then 1/2" pipe (or smaller) for the barrel is because 3/4" pipe is wide enough to drill the hole to connect the fire extinguisher to the base. We can't use 3/4" pipe for the barrel because the fire extinguisher's valve can only release small quantities of air, so the air won't be released fast enough to propel the projectile.

Step 3: Building

Now that we know how this air cannon works, let's build it! This is a pretty easy build and should be quick and painless. First, get your fire extinguisher. If it is a new one spray all the powder out into a bucket until all of the air pressure is gone. Then, unscrew the valve from the cylinder and empty all of the remaining powder. Cut off the plastic tube attached to the valve, and then screw the valve back on as tightly as possible.

After that, we need to make the base. Cut a short section of 3/4" PVC. Now, drill a hole with a 1/2" drill bit in the middle of the pipe. You will need to make the hole a little bigger by scraping the sides with a smaller drill bit (a Dremel might be useful). The nozzle of your fire extinguisher should fit very tightly inside this hole. Then, glue the 3/4" PVC end cap to one end of the pipe and the 3/4" female adapter to other side. After that, insert the nozzle of the fire extinguisher in the hole and put some epoxy around the part where the base and nozzle connect.

Put your Schrader valve in the center of your 3/4" PVC end cap. Glue this to your 3/4" male adapter using a small section of 3/4" pipe. Then, glue together your other 3/4" male adapter and the 3/4" - 1/2" reducer between a small section of 3/4" pipe. With these two attachments, we can fill up the cylinder with air and attach the barrel.

Note: the picture with the base attached to the cylinder has some flaws, yours shouldn't have a 3/4" coupling in the middle.

Step 4: How to Make an EASY "rifled" Barrel + Shotgun Conversion

Now that we have made the air cannon itself, we need to make the barrel(s). I will be showing you how to make a "rifled" barrel that can shoot .45 sabots accurately, how to make a shotgun shotgun shell you can use in a section of 1/2" pipe, and how to attach a smaller diameter barrel to shoot small projectiles like BB's.

For the "rifled" barrel all we need is a few feet of 1/2" PVC and duct tape! That's it! Simply cut three strips of duct tape as thin as you can and tape them straight on the inside of your barrel in a triangular pattern. Although this is very rudimentary, it actually works! You will see how accurate it is in the video at the end.

We also have to use duct tape to modify the .45 ammo a bit. Simply wrap a strip of duct tape around the base of the bullet until the bullet is a good fit inside the barrel. Instead of using the sabot in the box, use a small piece of paper towel and ram it in with a dowel. The picture above shows how big the paper towel sabot should be.

Now let's make the shotgun conversion. You will need thin cardboard, duct tape, the .50 caliber sabots, and some shot/BB's. First, fold a sheet of cardboard an inch long into a tube with a diameter of 1/2". Next, cut a circle a little bigger than the diameter of the tube, and tape/glue it on. Punch a hole through this circle. To assemble the shell, put in one of the .50 cal sabots; if it is not a tight fit then put some duct tape on the inside of the shell. Then, pour in shot/BB's until they fill the top of the sabot. "Crimp" the shell by densely packing in some paper on the top.

If you have a small barrel such as a .177 or .22, you can use it with this air cannon by putting some duct tape on the bottom so that it fits snugly inside the barrel attachment. The smaller the barrel is in diameter, the more shots you can get out of this thing. We'll get more in-depth about this later.

Step 5: How to Shoot the Air Cannon + Videos

Finally, we're finished! Just as a recap, here are the steps to firing the air cannon:

    • S on the Schrader valve attachment
    • Fill the cylinder up until the arrow on the pressure gauge points to the top of the green
    • Unscrew the Schrader valve attachment
    • Screw on the barrel attachment
    • Load the barrel
    • Put the barrel on
    • Lock the trigger with the safety that comes with the fire extinguisher until you are ready to fire
    • Rest the fire extinguisher on your shoulder like a butt and hold the barrel like a stock
    • Quickly pull the trigger (a quick squeeze is all you need)
    • The shots will have consistent velocity until the arrow on the pressure gauge goes to the red

    Here are some videos showing how to fill up the cylinder and some shooting (only one of the videos has sound, sorry about that):

    This video shows that the duct tape rifling actually works. You can see that the bullet wasn't wobbling around in the air because it made a nice round hole, so those strips of duct tape must be doing something. Hollow point rounds shred through cardboard! (has sound)

    This video shows what happened when I shot a bullet trap. Hollow point rounds make such large holes!

    This video shows the shotgun attachment and the spread. BB's have a very uneven pattern, I need some size eight shot!

    This video is a demonstration of how to fill the cylinder up.

    Step 6: Miscellaneous Project Ideas

    To wrap this Instructable up, here are some things I did with this project that aren't really specific to this project alone:

    I made adjustable iron sights, similar to the ones on an M79 grenade launcher. To make them, first, bend some rather thick wire into a "U" six inches long with the prongs one inch apart. Then, make a circle out of the wire with a diameter of an inch and wrapped it around the prongs of the U-shaped thing (you should be able to slide the ring up and down but it should stay where you move it). Tape the finished rear sight to the end of the barrel and put on a front sight. In order to use the sight correctly, you'll have to do some hand testing to figure out the drop at x range and how far to move up the ring. When you look through the rear sight and see the foresight, you will have to tilt the barrel up a little.

    I attached a 1/4" barrel to the barrel attachment by putting duct tape at the end until it fit in very tightly. I also added a bolt to easily load ammo, which holds a surprisingly good seal. A smaller barrel will allow us to fire more shots as it uses less air. Keep in mind that this project is very similar to a paintball/airsoft gun, but you can't spam shots with it like one of those simply because of the PSI; a paintball gun uses ten times the pressure we're using, which means that there is ten times the volume of air per square inch in the cylinder then in this air cannon. Our air cannon can still fire several shots without losing much pressure though, which is a lot more convenient than other spudguns, but it wouldn't be very good at an airsoft arena!

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    4 Discussions


    6 years ago

    I'm still trying to find the rifled barrel


    Reply 6 years ago on Introduction

    It's not rifling in the traditional sense, but I've come to the conclusion that those strips of duct tape are stabilizing the bullet. Here's my evidence:

    Ever played with nerf guns? Well, look inside the barrel of one of those snipers and you'll see thin, straight grooves inside. The darts still fly straight. Shotgun chokes use the same type of grooves to create a tighter pattern. If you watch the video where I shoot at the box, you can see clean holes, evidence that the bullet was hitting the target directly at the hollow point. When I shot at it with a smoothbore barrel, however, the bullet went close to where I aimed but the hole looked more like an outline of the bullet than an actual hole, evidence that it was wobbling. Although the rifling doesn't make the projectile spin, I think it's providing some type of stability and direction. Anyway, try this project for yourself, and if you have any evidence that the rifling doesn't work let me know and maybe we could come to a different conclusion.


    6 years ago on Introduction

    How bad did your eyes/nose burn when you emptied it? i dumped the powder out of an unpressurized one about 15 years ago and mine are burning just thinking about it.


    Reply 6 years ago on Introduction

    I went out in the woods and emptied it out in a bucket, my eyes didn't hurt at all. I think the reason why your eyes hurt so badly was because maybe they used different chemicals in the powder back then. According to Google, it's mostly baking soda. The one I used was a Kidde dry chemical extinguisher, but I think all brands have the same stuff if I'm not mistaken? Anyway, as long as you are in a ventilated area, you should have no problems with a modern extinguisher.