Potato guns

[Adama]

Seriously, how do I put a picture in my post?

[Mike Shaul]

I've owned both a combustible and a pneumatic, I liked the pneumatic better and thought that it *seemed* safer (I can't really tell); it was at least easier to use.

A few websites I've enjoyed (and still have bookmarked).

PVC Ballistics
Spudgun Technology Center

[lukevanoort]

I don't have one, but I'm looking into making one. It's next up on my list after making nitrogen triiodide, flash powder, and more gunpowder for 4th of July. (I've decided that fireworks prices are highway robbery) However, if I'm in Canada for the 1st, I won't be doing anything at all like that.

[Gabe]

[quote=lukevanoort]It's next up on my list after making nitrogen triiodide, flash powder, and more gunpowder for 4th of July. [quote]

WHAT?!?!

[JamesCH95]

I have several guns, but my favorite is my latest creation.

Fuel: Propane
Combustion Chamber: 4"Dx18"L
Interchangeable Barrels: 2"Dx3.5'L, 2"Dx6.5'L, 1.5"Dx4'L, 1.5"Dx6'L, all barrels have functional muzzle breaks.
Igniter: Lantern Flint

As for the safety of air over combustion... my air cannon was the only one to ever explode on me, and as long as proper construction techniques and materials are used, everything should be fine.

I did the calculations for the MAXIMUM IDEAL PRESSURE generated by the perfect combustion of propane and air... 132psi, well within the 220psi operational limit of the Sched 40 PVC I use.

[Pat McCarthy]

Just recently, I rebuilt the accumulator of my air cannon so I could enjoy it. I originally built it for a physics class projectiles project and never gave the PVC cement enough time to cure before I pressurized the tank, thus, why I had to rebuild it.



Anyway, mine runs off of compressed air pumped into the accumulator by a standard bike pump. I test fired it for the first time since I rebuilt the tank last week, and I have to say I love the results! I've been using pine cones and redskin potatoes as ammo, and I've had a pine cone go about 150 feet!

I also built an electronic trigger for the sprinkler valve, but getting to 24 volts with batteries takes a lot of batteries (Two 9 volts and four AA's in series). I have been using just 18 volts to run it, but it doesn't open the valve fast enough, so I've just been using the manual pressure release instead, with great results. So I'll probably just scrap the electronics.



My air cannon makes a very odd sound when fired, that I think has something to do with the shape of the inside of the sprinkler valve I'm using. But in any case, it's very satisfying when accompanied by the kickback of a firing.

On a side note, does anybody know the Michigan laws for air cannons? I've been unable to find anything pertaining to them through Google searching.

[Andy A.]

A friend I have an assortment of cannons. The most recent, and impressive, has made use of a lot of fancy shmancy threaded connectors, allowing us to try different barrel lengths and such.

The best results have come from a ten foot barrel. We can't buy lengths any longer, and frankly, couldn't handle the weight. It's heavy! The chamber is perhaps 18 inches in length not including fittings and fueled by propane. We have not yet metered the propane, and just open up an unlit torch for about 8 seconds. It's worked well enough that we don't feel the need to invest a lot of time and money in a metering pipe.

We use an old flint style igniter. We prefer this over electronic because it gives a huge spark. I've never felt confident sitting there clicking away at a barbecue lighter waiting for something to catch. With the flint, we know it'll go if there is any fuel in the chamber. It also adds a nice tactile feel to the cannon.

We've also got a nice little muffin fan on the rear cap. It seems to do a nice job of stirring up the chamber, and it sure makes it a heck of a lot louder!

The next project to perfect is the silencer. We had a good proof of concept, but it requires refinement. We just have to figure out how to keep it from spewing confetti everywhere.

-Local

[BBnum3]

My friends and I have built a couple of cannons, one for potatoes and the other for tennis balls. We had to order the 2 1/2" PVC special off of the internet. It's about 7 feet long and can shoot about 200 feet. We shoot it at night occasionally, and when we do that we pour some glow stick stuff on the balls so we can see them fly.