4 ms·
> > Who builds a pipe gun out of a plastic pipe? It would just blow up in your hands. > Someone who's aware that when a metal pipe bursts, you get shrapnel. >
by btrettel 7y ago
> > Who builds a pipe gun out of a plastic pipe? It would just blow up in your hands.
> Someone who's aware that when a metal pipe bursts, you get shrapnel.
> The potato guns I've seen tend to be made from plastic pipes for that reason. PVC is surprisingly strong for these applications. As a teenager, I've built some solid rocket motors with a friend, and we've been using plastic pipes for the same reason.
Mechanical engineer with potato gun experience here. Your statements here are not just wrong, but dangerous. PVC pipe is discouraged for potato guns specifically because of shrapnel:
https://www.spudfiles.com/spud_wiki/index.php?title=PVC_pipe https://www.spudfiles.com/spud_wiki/index.php?title=PVC_pipe
> One of the main disadvantages of PVC is that it becomes brittle in cold weather, which may lead to chamber failure, especially in pneumatic launchers. When PVC fails under pressure it breaks into sharp shards, which are propelled at high velocity. Because of this danger PVC pipe is not rated for use with pressurized gases, and the use in spudguns is to be regarded as outside of specifications. Shrapnel from failure of PVC can be fatal. The reason PVC does not shatter with water is that water is not compressible, so water stores very little energy. Air is compressible and stores lots of energy. As a result, pressure rated ABS pipe is a better choice for a spudgun, as it is rated for compressed air. You can find it online or at an industrial supply store. There have been reports of serious injury and death from exploding PVC pipe, even at low pressures. Alternative materials, such as ABS, copper, and steel are much better choices.
Potato guns are typically built from PVC pipe because PVC pipe is cheap, PVC pipe is readily available, and most people building potato guns don't know better. The more knowledgeable folks tend to avoid it in my experience. Metal pipe would absolutely be stronger at the typical thicknesses of plumbing pipes.
- TeMPOraL 7y agoI didn't realize that, thank you. It seems I've been severely misinformed in the past about the dangers of different pipe materials for spud guns and rocket motors.
- btrettel 7y agoUnfortunately common practices in many hobbies are rather dangerous. I cringe when I see dangerous practices in hobbies I'm familiar with, and I freely admit that I've done the wrong thing before out of ignorance. Another aspect of the problem is that while many people are diligent about using pressure-rated pipe, they accidentally end up using non-pressure-rated fittings. I myself have fallen into this trap before in some projects of mine, and I didn't recognize it until I started learning more about potato guns. When making a project like this I typically go for all metal construction when possible because the components are stronger and the pressure rating is usually easy to find. For plastic fittings you need to familiarize yourself with the various markings that indicate the fitting is pressure rated. And even then that doesn't tell you what the rating is. In my experience, the pressure rating of a fitting is always lower than that of the pipe the fitting attaches to.
- jandrese 7y agoWhen I was a kid we built tennis ball cannons out of soup cans duct taped together. You take off the top and bottom of 4 cans and smooth out the edges. In a fifth can you punch several holes in the top and one matchstick sized hole on the side. Duct tape them together with the hole can on the bottom. Then you push a tennis ball down the barrel, squeeze a few drops of lighter fluid in the hole, swirl it around a bit and hold a lighter up to the hole. Done right it will chuck a tennis ball a couple hundred yards. I guess it might explode and shred everybody nearby with sharp metal can fragments, but the whole thing is pretty low energy so probably not.
- TeMPOraL 7y agoFWIW, the fittings I used in my teenage-years rockets were usually gypsum or plastic + lots of duct tape (for the rockets made from vitamin fizzle tablets containers); their pressure rating was "looks like it should survive the launch, but we'd better move back a couple meters and duck behind cover, just to be sure").
- anfilt 7y agoThe PVC in the picture can't be a potato gun. They need a larger chamber behind the barrel for either hair spray or compressed air. This looks more like storage container to keep stuff dry from moisture in the soil. Not only that the police claim it was a firearm because they found an old round of ammunition in the dirt. That pipe in the picture has 43 mm stamped on it for diameter. No small arm ammunition could even use that as a barrel. The only thing would fit in 43 mm tube would grenades, mortars, cannon or artillery shells. This guy should not be in jail for firearm offenses and he really needs a better lawyer. The police are just being stupid here or just trying to save face.
- sizzle 7y agoWe would spray axe body spray in the chamber, cap it, shove a Spud in the long barrel, and use a BBQ ignition wire to launch the potatoe hundreds of feet. One time the cops detained us but thank God we had a Physics AP book and explained we were learning about forces in motion etc. and got a warning. I imagine you would be facing serious time pulling a stunt like that today as a high schooler armed with a PVC spud canon in the suburbs...