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high speed (hope fully super sonic) PVC gun FAIL!!!! pics

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: DYI » Wed Dec 09, 2009 9:06 pm

Remember lgg's shoot at hundreds of kilometers a second he is going for 1125+ fps


No LGG that I'm aware of has ever fired at over 12km/s, and most are limited to under 8km/s.

If the goal is speeds over SOS, helium expansion or hybrid are the easiest routes to take. If novelty is the aim, and this could be constructed so that the piston survives repeatedly, it may be worth pursuing. It can be done by springer air guns, so it should be possible with an air spring.
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Unread postAuthor: Mr.Sandman » Wed Dec 09, 2009 9:12 pm

DYI wrote:
Remember lgg's shoot at hundreds of kilometers a second he is going for 1125+ fps


No LGG that I'm aware of has ever fired at over 12km/s, and most are limited to under 8km/s.

If the goal is speeds over SOS, helium expansion or hybrid are the easiest routes to take. If novelty is the aim, and this could be constructed so that the piston survives repeatedly, it may be worth pursuing. It can be done by springer air guns, so it should be possible with an air spring.
Hmm in the demonstration videos of the uhmw rounds by jagerbond they show the materials rigidity and overall strength. This would make an ideal piston. and if done correctly it could rival the speeds produced by you or larda's hygac20. The only problem would be the cost. But even thhough these things are true, i do beleive that he was trying to see if he could do it with such simple materials. The effect was inevitble. It is just not within most peoples means. which i guess goes back to square one when you sai that any attempt that is kept under 1 km/s is utterly pointless.
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Unread postAuthor: jhalek90 » Wed Dec 09, 2009 10:32 pm

Yes, a major deciding point in the construction is that is was 10pm here, and all my hardware stores were closed. :-(

So i simply got board... and wanted to test out the idea that had been plaguing my brain all day.

side note....
MY higher pressure (300-500 psi) steel gun was tested with ammo for the first time to day at 400 psi.

Shot AA battery through a steel cake pan, and then into a aluminum box.
Both target were very thin.... but i still smiled from ear to ear., :lol:

Also,
i have a very strange phenomenon that i need help explaining.
I shot a pop can.... very clear exit hole.... no entry hole.????
i just need to see if i can replicate it on command....then pics+video!!!
woot.
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Unread postAuthor: psycix » Thu Dec 10, 2009 5:39 am

Ragnarok wrote:a lightweight piston

Why?
It's the momentum that creates the pressure spike (at least, if you want the pressure to spike higher then the initial pressure source.)
If one would take an imaginary "weightless" piston there would always be an equilibrium of pressure, so it won't spike up higher.
A very heavy piston keeps compressing the air even while the pressure is higher then the driving pressure.
Of course there are limits, the piston also need speed. But I think piston momentum is an important aspect.
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Unread postAuthor: inonickname » Thu Dec 10, 2009 6:02 am

Mr.Sandman wrote:
DYI wrote:For a two stage gun to be of any great utility, you're going to need a burst disk separating the pump tube from the barrel.
Remember lgg's shoot at hundreds of kilometers a second he is going for 1125+ fps.


Not really, light gas guns usually tend to peak under 10 km/s after which human propellants become insufficient to drive the piston hard enough.

Why?
It's the momentum that creates the pressure spike (at least, if you want the pressure to spike higher then the initial pressure source.)

In conventional light gas guns the pressure of the working fluid is not the limiting factor generally. It's the speed of sound in the working fluid. A heavier and slower piston will LOWER the shock heating caused by the motion of the piston, which is the reason for having the piston.

However in a comparatively extremely low pressure scenario it is up for debate as to whether slightly higher pressures are worth the drop in temperature. A heavier piston is also more difficult to bring to a stop without damage to equipment. Finally, materials such as HDPE are used in conventional guns as plastics are fairly cheap and easy to have turned to the correct size. Important seen as these guns aren't known for piston lifespan.

It's also worth noting that a light gas gun is hardly the most efficient machine ever. You have substantial losses through the piston, and then again through the new working fluid and then again through the projectile. The only purpose for constructing a gun like this is pure muzzle velocity.

which i guess goes back to square one when you sai that any attempt that is kept under 1 km/s is utterly pointless.

Not really. There is more than one reason for building a gun whether it be scientific research, for the experience, a personal challenge, building to criteria, improvisation..the list goes on.
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Unread postAuthor: Ragnarok » Thu Dec 10, 2009 8:38 am

Mr.Sandman wrote:Remember lgg's shoot at hundreds of kilometers a second he is going for 1125+ fps.

Nothing shoots at hundreds of kilometres a second - the record so far as best I know for a "significant mass" is 42 km/s.

Significant mass being something more than just a few nuclei or something. Something you could actually weigh on a set of scales, even if it is an expensive scientific set.

psycix wrote:
Ragnarok wrote:a lightweight piston

It's the momentum that creates the pressure spike (at least, if you want the pressure to spike higher then the initial pressure source.)

Nope, it's the energy. (However, the inertia does help avoid piston bounce) It's force times distance we're talking about here, not force times time. The other thing is that we want to compress the gas faster, not slower.

Not that I'm saying that you want an unbelievably lightweight piston (because then it can't have much energy), but you don't want a heavy one either.
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Unread postAuthor: Mr.Sandman » Thu Dec 10, 2009 5:15 pm

Ragnarok wrote:
Mr.Sandman wrote:Remember lgg's shoot at hundreds of kilometers a second he is going for 1125+ fps.

Nothing shoots at hundreds of kilometres a second - the record so far as best I know for a "significant mass" is 42 km/s.

Ok for the record i totally just pulled that number out My culo. all this talk of railguns and what not has gotten to my head. I dont know why i said that.But anyways as i was saying to dyi in the chatroom, the cost of the materials and the constant maintenence required for these types of guns is horrendous. Its not technically pointless because that is a matter of perspective and opinion. All i was trying to say in the most unnecessary and complex way was that pvc was unsuitable for these types of guns and that they are not just spare parts guns.
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