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Lowest Pressure to break SOS?

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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Lowest Pressure to break SOS?

Unread postAuthor: boyntonstu » Mon Nov 23, 2009 12:06 pm

What is the lowest pressure that has been used to propel a projectile weighing at least 25 grains beyond the SOS?
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 23, 2009 12:17 pm

Depends how long you're prepared to make your barrel ;)
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Unread postAuthor: boyntonstu » Mon Nov 23, 2009 12:31 pm

jackssmirkingrevenge wrote:Depends how long you're prepared to make your barrel ;)


Thanks for the GGDT prediction.

My question was about what was actually shot and recorded.



When I saw 730 fps at 100 psi, I began to think SOS.
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Unread postAuthor: Technician1002 » Mon Nov 23, 2009 7:32 pm

boyntonstu wrote:When I saw 730 fps at 100 psi, I began to think SOS.


:D I'm working on the same thing. Bigger valve is on the workbench.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 23, 2009 7:54 pm

On a related note, I added some substantial reinforcement to the chamber of my 6mm burst disk pneumatic to allow testing at 800 psi, scheduled for tomorrow :)
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Unread postAuthor: rcman50166 » Mon Nov 23, 2009 8:06 pm

I may have cheated...
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 23, 2009 8:18 pm

Definitely not...
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Unread postAuthor: Technician1002 » Mon Nov 23, 2009 10:28 pm

jackssmirkingrevenge wrote:Definitely not...


LOL.. I had to look at that one twice to notice the decimal points are on the top.. :D
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 23, 2009 11:20 pm

Technician1002 wrote:LOL.. I had to look at that one twice to notice the decimal points are on the top.. :D


Yeah, I could have made a better job but believe it or not I actually have better things to do :P :D
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Re: Lowest Pressure to break SOS?

Unread postAuthor: Ragnarok » Tue Nov 24, 2009 8:02 am

boyntonstu wrote:What is the lowest pressure that has been used to propel a projectile weighing at least 25 grains beyond the SOS?

In a pneumatic using air... I have no idea.

There are few claims of supersonic pneumatics I believe. And most of those are air rifles. So few have fired projectiles of that weight, or have used other gases.

People need to get it out of their head that SOS in a pneumatic is something that happens easily. GGDT is far too generous in the number of 1100+ fps numbers it churns out.

Indeed, the way I've got Apocalypse set up means it won't give a supersonic velocity in Zero-D single stage modelling, where the maximum conceivable output is Mach 1 (and it'll only give that under ideal circumstances).

It's only when the modelling is changed to pseudo two stage (ideally, One-D), that supersonic velocities can happen at all, and it's still a veritable nightmare to actually coax such a number out of it, taking a lot of finely tuned numbers and no small amount of pressure.

I would go to Apocalypse now and actually do some of the numbers - but all of that stuff is on my laptop, which... you guessed it... is still in servicing.

~~~~~

Anyway, as something of an answer, the pressure required will vary so wildly with launcher design that actually giving you a number would be moot.

Also, whether or not you have the theoretical potential, practical achievablity will vary massively with barrel length, calibre and projectile mass (Imagine someone asking "what pressure is needed for my launcher to do 700 fps" with no more information present).

Whatever the exact answer, it will not be low. It takes a lot of pressure even with something designed for it.
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Unread postAuthor: iknowmy3tables » Tue Nov 24, 2009 9:34 am

OH wait thats right :) , I don't know what pressure it was but it was probebly with hydrogen or helium, HA I bet you guy's forgot about that one, hehe beat you all to it :lol:

yes I have seen fast speeds obtained by giant barrel setups, I once met another spudder who built pneumatics which was cool accept for that fact that he built this gigantic pvc gun with two 4" pipes 12ft long for a chamber and a really long barrel I think it was 12ft or 17ft I don't know, but anyways it was constructed entirely out of DWV fittings and used a 2" pvc ball valve, anyway it annoyed me so figgin much that his gun was chronoed 600-700fps, while my well constructed modded sprinkler valve gun wasn't any were near that. since then I feel reluctant to build another large spudgun unless it beats his. sorry I digress, the point is ridiculously oversized setups can shoot pretty fast but their ridiculous
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Unread postAuthor: psycix » Tue Nov 24, 2009 9:51 am

If you HAVE to break the SOS with room temperature air, you can always use a gun that shoots a gun... :D
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 24, 2009 9:55 am

Hopefully not a case of hubris but within the next few hours I hope to have some concrete mach results on unheated air :)
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Unread postAuthor: jeepkahn » Tue Nov 24, 2009 10:02 am

lol... ping pong vacuum cannons approach sos... ping pong ball weighs 41grains... pressure used 14.7psi aka atm....
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Unread postAuthor: Ragnarok » Tue Nov 24, 2009 11:22 am

jeepkahn wrote:ping pong vacuum cannons approach sos...

Emphasis on approach. They can theoretically get very, very close, but they won't go supersonic.

iknowmy3tables wrote:but it was probebly with hydrogen or helium, HA I bet you guy's forgot about that one, hehe beat you all to it

Damn, one and a half hours after I said "or have used other gases", you beat me to saying it.
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