"Spud Guns" aka Potato Cannons, etc... (PIC HEAVY!)

I have a side hobby of backyard science, usually involving cannons.

This started as an adolescent/teenage obsession with "spud guns", and worked up from there.

I was just wondering if anyone else here has built or plays with home made weaponry.

This is my latest cannon.
It's constructed of ABS plastic (painted black) and burns a calculated propane/oxygen mixture. It has a meter system (made of brass plumbing parts) to measure out the correct gas mixture.
The ignition system consists of a BBQ grill sparker wired through a motorcycle ignition coil, wired to five spark gaps in series inside the chamber (this gives more even ignition than a single ignition point).
There's a modified computer fan inside the chamber that aids in mixing the gases together, and in venting the chamber between shots. The large valve is for venting the chamber.
Note: the rear grip shown is a temporary and has been replaced with one matching the front grip.

http://img86.imageshack.us/img86/7900/img1897jy9.jpg

http://img443.imageshack.us/img443/1657/img1898tj7.jpg

http://img221.imageshack.us/img221/9603/img1900ov8.jpg

http://img135.imageshack.us/img135/4405/img1903yk6.jpg

It's shown with a 5 foot 1.5" barrel, but the barrels are interchangeable via the breech loading system pictured above.
I've found some pressure rated PVC pipe with an inside diameter just a few hundredths of an inch larger than the diameter of a golf ball - makes an excellent barrel. I have 5, 8, and 10 foot lengths of it.

According to my math (and a friend's chronometer to confirm), on a "good shot", it will get a golf ball (which weighs 46 grams, or about 700 grains) going just shy of 680 mph (or 1000fps) for a muzzle energy of around 1,550 ft/lb. Although, because a golf ball has a pretty low sectional density compared to a metal bullet, it will loose velocity (and energy) much faster than a bullet would.

Here's a "damage shot" on an empty 1 gallon olive oil can, from about 25 feet.

Entry:
http://img146.imageshack.us/img146/6051/img1916bf3.jpg
Exit:
http://img231.imageshack.us/img231/1127/img1915an1.jpg

It will put a golf ball clean through a phone book and into the second one behind it.

I've experimented with "solid propellants" (such as guncotton or black powder in the bottom of a hydraulic cylinder) but find the expense and danger don't outweigh the results.
My propane-fueled gun is reliable, easy to reload, very cheap to fire, legal in most states, and lots of fun! Also sounds about like a 12 gauge.

The local Sheriff has been out to visit me 4 times due to noise complaints from my neighbors - in each case I showed them the cannon, showed them a printed copy of the laws stating that "potato cannons" are not destructive devices or firearms, and they let me be. In fact, twice the responding officer asked if he could try it out, which I happily obliged :smile:

Anyone else here share my interest in backyard ballistics?

Peace,
Pete Zaria.

Exellent. Looks like fun ! Ive built and played with several potatoe guns but none of them were as sophisticated as yours.

My favorite toy is a replica of a Coehorn motar that I built that shoots coke cans using black powder. It does make a big bang complete with fireball and smoke.

nice one :) I've always wanted to make one of those

Quote:

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Originally Posted by HotGuns

My favorite toy is a replica of a Coehorn motar that I built that shoots coke cans using black powder. It does make a big bang complete with fireball and smoke.

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I'd love to see pics if you wouldn't mind posting them :)

Quote:

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Originally Posted by stickybeatz

nice one :) I've always wanted to make one of those

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Thanks :) Believe it or not the total project cost was under $200 and build time was around 10 hours including "tuning". If you want to build one let me know and I'll give you some relevant links and personal tips.

Peace,
Pete Zaria.

Be careful! My brother in law built a potato gun out of cheap stuff from Home Depot (ABS and Glue). He used hair spray as an explosive propellant. Worked fine for the first couple dozen times, then when he let a friend's kid try it, the thing disintegrated, spraying the poor boy with plastic shrapnel. Now he's looking at a huge personal injury lawsuit.

Quote:

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Originally Posted by AZ Husker

Be careful! My brother in law built a potato gun out of cheap stuff from Home Depot (ABS and Glue). He used hair spray as an explosive propellant. Worked fine for the first couple dozen times, then when he let a friend's kid try it, the thing disintegrated, spraying the poor boy with plastic shrapnel. Now he's looking at a huge personal injury lawsuit.

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I'm very sorry to hear about your brother in law's situation. I hope that boy makes a full recovery and your brother in law doesn't have to eat a big settlement.

I've pressure tested this rig to 25% more than the peak combustion pressure should be, without any signs of failure.

ABS shouldn't shrapnel if it fails, it should "rip" open cleanly - quite a bit of testing has been done on this and that's why I selected ABS instead of PVC. Are you sure your brother in law didn't use PVC?

There are a lot of variables there - did he prime and glue the fittings properly? Did the pipe "bottom out" in the fittings, as it should? Did he let them dry a full 24 hours before first use? Was the pipe NSF-PW pressure rated (not NSF-DWV, which isn't safe for use with pressurized gas)? Etc....

Thanks for sharing your experience.

Peace,
Pete Zaria.

I made one years back (12-13 years ago)...first discovered a 'potato gun' on a hunting trip...we had a ball.
Mine was pretty rustic, but could shoot a spud plug quite a distance.

Yours is unbelievable...you must be a 'rocket scientist'...:rofl:

Enjoy...

We could have worked that pic into the potato marriage thread a few day ago...:yup:

Stay armed...stay safe!

Pete you must be a modern day Henry Ford. I think you should post a video on youtube showing us how it works.

Thats some wicked cool stuff. Dont shoot your eye out kid.

Heres the only picture I have left...
http://i18.photobucket.com/albums/b1...s/IMG_0523.jpg


Made it a few years ago,I've had a lot of fun shooting concrete filled coke cans a few hundred yards...

Thanks for the compliments, guys :smile:
I might do a youtube video when the weather warms up.

Peace,
Pete Zaria.

I dont know why that came out so big...can somebody size it down?

@HotGuns,

You made that?! Did you use a lathe/mill to build the cannon itself? Looks EXCELLENT. I'm sure the performance is great with a decent black powder charge under a coke can.
I've filled caulk tubes with concrete and taken down small trees with them - I can only imagine what a concrete filled coke can would do. Nice.

Peace,
Pete Zaria.

Lathe mostly. Made some dies for the trunnion caps and pressed them using a haydraulic press. Used a mill for the touch hole and a bandsaw for the oak. Its made out of 4140. Used all thread for the elevation and turned the brass handle and milled it.

Havent tried to hit anythig with it really..mostly just shoot it out in a cow pasture. When I measure out the powder charge, it'll keep the cans within several feet of each other.

Amazing work, your craftsmanship shows. I'd love to see a very similar one with a longer barrel :smile:

How big a charge do you feel safe putting under a concrete-filled-coke-can?

Peace,
Pete Zaria.