Picture of High Pressure Metal-Slug Cannon
Feel like breaking something? A fence, a TV, a car-door, or simply disintegrating a potato flying 200 feet per second? All this is possible with your own high-pressure copper slug cannon.

There are plenty of PVC and ABS potato-gun guides on the internet, this guide aims to create something a little different. While it can fire potatoes (though they shatter), or anything that fits into a 1" barrel, it allows the use of extremely high air pressures to fire wooden, plastic, or metal slugs. Creating a metal cannon is more safe, far more capable, and as a consequence, more expensive.

While PVC can explode and shatter under high pressure (120< PSI), and ABS can split under medium pressure (70< PSI), copper can take far higher loads before failing. Rather than use combustion for power, this design uses compressed air. If the pressure goes too high, a copper weld will crack to release the air, rather than send out fragments like PVC. Copper also does not fatigue like PVC or ABS. The difference in strength between 110 and 150 PSI is immense, and 150->180 is even more extreme. Though like anything, the assembly has its limits, keep it under 350 PSI.

The cost ended up being around $100, and while the project is not very difficult, it is time consuming. If you feel the push to create an assembly of potential destruction, I encourage you to learn from, modify, and get to work on making your own copper slug cannon.

***Liabilities ***
Slug Cannons and Potato Guns while very fun, have the potential to kill. We are dealing with a high-pressure design that is effectively a weapon. Use common sense, don't point it at people, cars, someone else's property, or anything else that can get you in trouble. With a wooden or metal slug, you really can punch through a car door, or break a person. By reading this you agree not to sue me for anything ever, including but not limited to any grief you cause yourself and others from the information in this guide. That said, have fun!
***End Legalese***

***Laws in California ***
These are the laws for this assembly in California, it's complicated, but legal.

Potato/Slug-Guns/Zip-Guns that use combustion, such as hairspray, propane, or butane, are illegal, since they are a non-licensed manufactured firearm. Using compressed air avoids this rule, and there is a second condition this assembly does not meet: fixed ammunition. A fixed round is a round that contains propellant, casing, and bullet all in one container. For this, there is no case, and the propellant is contained in the rear chamber, not on the slug, thus, it isn't a fixed round. Under ATF (Alcohol, Tobacco, and Firearms - Federal Law) it is legal.

Under California state law, there is a law which could be charged against you, called destructive device law. Any round over 50 caliber (which slugs definitely are) is a destructive device, if it is used with the intent to destroy something that would be an illegal act, like targeting a person or a car. Shooting a wooden target or dirt is not malicious intent. There is another technicality, smooth-bore (non-rifled) weapons that are muzzle loading (which this slug cannon is), are not destructive devices. This effectively puts it in the same legal category as an air-soft gun, despite them being very different (though air-soft guns are not muzzle loading).

Now realistically, when this fires at 150 PSI, the round whistles, a ton of water vapor pours out the barrel, and an echo is heard a half-mile away, which many people would report as a rifle or shotgun being fired. Most police will be very cautious, but likely tell you to stop and go do something else since they received complaints. Some police may confiscate the assembly or even arrest you, whereupon you go to holding, and will be let out after an hour or two and get your cannon back. In court, you will definitely be o.k. However, this is a huge hassle, and no one wants to go to a holding cell. Within a city, you will likely violate noise limitations or public-disturbance laws, which you can be fined for legitimately.

ATF laws [Title 18 United States Code (U.S.C.), Chapter 44, S 921(a)(3)] and [26 U.S.C., Chapter 53, S 5845] should be printed out. They define the classification of a firearm.

California state laws [CPC 12090-12094]; [CPC 12085-12086]; [CPC 12020] discuss the rules and classifications that relate to this assembly.

Simply put, it's legal in California, many cops think all potato guns are illegal since most are combustion, go fire it out in a rural area to avoid noise laws and attention. Print them all out, and keep them with you in case cops show up, and be friendly. CPC 12020 is the one that most police will be suspecting against you, and strongly emphasize that the assembly is compressed air.

Whew*, lots of information.
***End California Law***

Now let's get to building!
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BroW12 months ago

While I could be and quite possibly am wrong...the explanation given to me was that since potatoes were not "solid shot" they were considered legal, where as a solid shot such as a golf ball (or your slugs) is illegal and a BATF violation. Im in Tenn. so thats all I can speak for, but I would check VERY VERY carefully before letting the LEOs catch me with this. HAVING SAID THAT its beautiful :)

-CCCP-9 months ago

I put the instructable in the comments! Your instructable rocks. I am making mine with a flanged ball valve and the camber on the bottom. I based it off of this:

I made these high powered SteamPunk cannons using Steel pipe and fittings that were laying around (Free) although if you do not have accese to a steel yard or steel fittings, this project is probaly to expensive for you :(. Just layed out the peises until I liked the look of it [longer barel, large tank/air capacity, and trigger valve position are things to pay attension to], and put the pieses togeter using teflon tape, a vice and a pipe wrench. The main reason to using steel piping it the finished cannon is a lot safer than PVC (at high pressures) and I personaly like the over all look and feel better (a little weight good)

Air Cannon- My record distence was 249 feet (76 meters) with 125 psi at about 45 degrees.

Paint Ball Cannon- Shoots at about 100-150 fps (one round at a time)

While the spring operated ball valve is significantly better than opening it by hand, you're still not getting even close to the amount of force that the high pressure is really capable of. Make yourself a piston valve and you'll find that at half the pressure the rounds will be moving just as quickly as they do from this model. A good piston valve snaps open so fast that it makes a bang even when firing empty at pressures as low as 15psi.

NightHawkInLight, For tight fitting projectiles the high flow of a ball valve is required.

I looked into making a piston valve, all the designs I found were only for PVC assemblies, which would crack or shatter at 160 or 240 PSI. The more common sprinkler solenoid designs were again, made of PVC. I'm just terrified of PVC shrapnel going into someone, or the person holding it.

If you know of any references, resources, or materials that would help me make a strong, high-pressure valve, I'd greatly appreciate it and would get starting on building one, and updating the guide.
Well really you can build a piston cannon out of copper the same way you would out of PVC. The only challenge is finding or making a piston that will fit relatively snugly in your pipe. it's not really a big deal to change what the pipe is made out of. You can see one of my designs in a video I made about three years ago:

I've made some adjustments to it since then, such as adding a thicker rubber washer to the piston and cutting a groove around it for an O ring, but in general it's the same. Works great, and it would still if made from copper.
Mr_Rep9 months ago

would a sprinker valve work instead of the ball valve? If so, would i have to modify it?

QuackMasterDan (author)  Mr_Rep9 months ago
I have not written any new guides in over a year. I am that this very moment writing a new guide, the successor to this slug cannon. One that is cheaper, simpler, smaller, and about 40% more powerful due to being more efficient by better air chamber design, and by using a solenoid electric valve. A sprinkler valve will not work due to it failing (Shattering) above 90PSI. If you aren't going over 90PSI, then yes, it would work, but why make a copper cannon with PVC parts? In two weeks I'm hoping to have the new guide up. Thanks for the comment =]
TK Trooper9 months ago

You have to make and send me one

DanTDM1 year ago

I know: Use this type of ammo:

Cut drinking straws into 2 inch lengths. Bundle a bunch up with packing tape so it is the right size for your barrel. The outside should be quite round. Slip a pull string firework into every straw (cut the string off first) and hold the fireworks in place with glue. Put a little hot glue in the other end to seal it. Load it in, glue side first and fire! The ammo will explode on contact.

-CCCP- DanTDM9 months ago

That can win a war.

-CCCP-9 months ago

Mine has a 1/2 inch barrel. The ball valve is stainless steel. The valve is 3 piece for easy repairs to the seal. Maximum pressure is 750 psi. I use a 300 psi stock pump to pump it up or a 250 psi air compressor.

DanTDM11 months ago

Mine is steel pipe with a different design. It can go up to 600 psi (from a fridge compressor)

johnny1081 year ago
Nicely done- I'm in mid-build, but I thought of a few ideas:
1. Have you ever considered the accuracy of the system? A projectile with fins? (Like
the Frag-12 shotgun round, or the WW2 style disposable panzerfaust)
2. Sabot projectiles- cut the wooden dowel slug into quarters, with a central hole that fits,
for example, a dart made out of a standard bar room dart with more rigid fins? Or
maybe a "cup" that holds some steel shot, for bird hunting?
3. You use hot glue as a filler for the weight of a projectile. Have you tried using
solder, or a melted fishing or wheel weight?
4. I've worked with high pressure tanks in SCUBA gear- for safety, have you ever
thought about wrapping the air chambers in fiberglass matting, filled with
epoxy resin? Like the light-weight air bottles firefighters use? If a pipe bursts,
The matting might help to contain the fragments.....(this is easy to find as a boat
patch/repair kit). Even wrapping the tubes in twine and covering them with epoxy,
etc. would help. Although- this would hide stress bulges, and cracks....
Thank you for this epic Instructable...........
willnate johnny10811 months ago
how about spring steel fins that pop out after coming out of the barrel?
johnny108 willnate11 months ago

Steel fins that spring out would work (that's how the RPG-2 works). The problem would be making the design fast enough to be accurate, and quality control to ensure all fins come out at the same time. Easy to do with machined aluminum in a factory (RPG-7s), but not so easy at home.

Sabots can be made easily with a hole saw drill bit the same diameter as your barrel. You drill out a chunk of wood, take the bit apart, and remove the little piece of wooden dowel, with it's perfectly aligned center hole (enlarge, if needed), and cut this in half, lengthwise- giving you 2 halves with a perfectly centered middle hole for the projectile. A turn or two of aluminum foil holds this together, and increases the diameter as needed, tearing away when it leaves the barrel. For longer projectiles, just make two of these sabots.

QuackMasterDan (author)  johnny1081 year ago
We considered a few different accuracy methods, and sabot was the only one that seemed practical, but too much work for repeated shots. Rifling the barrel is... challenging, the tools for which, at a bore of 1", you may as well just buy a musket.

Oddly enough, though we didn't have them at the time, sanding down a golf-ball with a belt-sander worked really well. They spin like crazy, but are a lot of fun.

The cannon is meant to be something fun to just take out to a field and break random objects with. Just for fun. If you're able to find a practical use for it, I'd love to hear about your results.

You have a lot of ideas for how to improve this instructable. They are practical, applicable, and well-thought-out ideas. Have you considered making any instructables of your own?

It brings me great joy to know that you are having fun following this guide. It's fun to plan and design and build, but my designs can only go so far. It's so neat to see others take up the mantle and keep the good ideas flowing. Thank you for the positive comment =D
Using foam coffee cups as the sabot, and loading this with normal airgun BB's, you can make an effective system to bag waterfowl, or game birds, in a third world country (Afghanistan).
As you said- rifling the barrel is a problem- so the projectile must improve- still working on that.
Not really sure if I should make an instructable. I've been an 89Delta for 8 years now (The U.S. army designation for an EOD worker- I'm in the army's bomb squad), that kinda focuses me in one direction.....Weapons with real world applications.
bcavaciuti1 year ago
very nice...gonna try an make one this weekend though with a few personal modifications because i can. from the kick you were getting im definatly gonna make a wooden stock and securly attach it to the rifle, probly incorperating the air chamber into it or below it as the handle/trigger mount, and some iron sights or if i can spare the money buy some real rifle sights. make it out of the smaller caliber copper tubing coz ive got more of that but awesome yours is probably the best ive seen for a human pumped version.
SGT. Desert2 years ago
nice but damm you my tv is brocken
do you think i could use threaded piping instead if i had thread locking cement?
QuackMasterDan (author)  builtbyben982 years ago
It's unlikely you would need locking cement, you're just holding pressure. But some sort of putty would be necessary to well, hold in the air.

I initially looked into building this with threading piping, and it became extremely expensive very fast.
would a soldering iron (without a flame) work?
QuackMasterDan (author)  builtbyben982 years ago
If you're connecting copper pipes with solder, you're definitely going to need a blowtorch. It's not just about melting the solder, the pipes also need to be hot to bond to it. A blowtorch is required, and is actually pretty easy to use. Be sure to buy leather gloves!
Cdn Sapper3 years ago
I was looking at, and liking your design, one suggestion though, as you were saying that pressures exceeding 350 psi could cause a failure in one of the sweated joints, have you considered incorporating a relief valve in the system, that might blow safely at a lower psi rather than risk damaging your cannon and potential injury. I quickly googled "high pressure 1/2 inch relief valve 270psi" and hit one site that showed relief valves from 25 to 5000psi.
jonnyd553 years ago
I have always wondered if it was possible to make one of i know :) great work. how about increasing the danger and launching a lit fire work......hilarious, dangerous, very silly and probably must be done!
QuackMasterDan (author)  jonnyd553 years ago
Lit firework down the barrel. That sounds like a ton of fun! I hope you have a long fuse =]
kretzlord3 years ago
haven't even read the "steps", but i have to give you kudos for your knowledge of the laws involved with your project. The project looks awesome, so i shall read on...
ilpug4 years ago
I find it funny that the much weaker combustion cannons are illegal, while the much more powerful air cannons are allowed.
QuackMasterDan (author)  ilpug4 years ago
Laws can be funny that way. For some odd reason, things that are illegal, often end up being very fun, including potato-cannons, homemade fireworks, file-sharing, speeding, and a limitless amount of other great activities.
Just because it is fun, you shouldn't do it if it's illegal. Unless you live out in the middle of nowhere where no one cares.
mr. clean4 years ago
oh man if u really want to get crazy buy 1.5" or 2" steel gas pipe in 6 foot sections and use reducers and a plumbing pressure tester on one end for filling and the proper size ball valve for pressure release on the other. iv'e made 2 air cannons with these materials, it wasn't exactly cheap but the results are astounding. my largest is 1.5" barrel with a 1.5" air chamber and its around 13' long. i fire rocks and anything else i can find. when rocks are fired they are usually accompanied with sparks. also try to keep your air chamber the same volume as your barrel or a little larger. mine are also muzzle loaders but i don't use a ram rod i just unscrew the barrel each time and i pack a wad in the barrel to keep air from leaking around the projectile. that's my 2 cents on the subject.
classtopher4 years ago
Not intending to be a safety nut here, but if you or other readers were interested in adding a "safety" to prevent accidental firing you could add a second valve before or after the ball valve (trigger valve). If you used a screw valve like on a hose spiggot then it would take several turns to turn the safety on or off. When the safety valve is closed it cannot fire if you accidentally hit the ball valve.
QuackMasterDan (author)  classtopher4 years ago
Thanks for the suggestion, I may integrate it into future designs.