"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.
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.
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?