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Small coaxial

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: rixth » Fri Oct 26, 2007 5:48 am

That'll hold to 150psi?

The other thing I worry about with a metal coaxial is that the pressure of the gas pressing on the walls of the barrel might make it implode. Has this even happened?
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 26, 2007 5:54 am

rixth wrote:That'll hold to 150psi?

The other thing I worry about with a metal coaxial is that the pressure of the gas pressing on the walls of the barrel might make it implode. Has this even happened?


good epoxy will hold, I take my epoxied pneumatics to 400 psi :)

The amount of force required to make your copper barrel implode is much higher than any pressure you'll manage to reach with a bike pump ;)
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Unread postAuthor: rixth » Fri Oct 26, 2007 6:01 am

One final thing... those small compressors (ie, ones with no tank), how long do they take? I know its a while but yeah.

My chamber is 97 cubic inches.
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 26, 2007 6:04 am

they're sh!te, buy yourself a good stirrup pump like this one and get more pressure faster with some good exercise to boot :D
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Unread postAuthor: cwazy1 » Fri Oct 26, 2007 10:26 am

lol Jack, i've gone through 3 of those pumps at 40$ a pop. good thing is that i've gotten my refund for each and every one of them.

if u do decide to get one of those bike pumps, get a good one, or else it'll break really fast.
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 26, 2007 12:04 pm

hehe I didn't mean that specific model :P :D
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Unread postAuthor: battlemonkey » Fri Oct 26, 2007 12:52 pm

Yeah, my old bicycle pump i could get to go to 160 psi and it wasn't a shock pump :!: . they do break eventualy.
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Unread postAuthor: rixth » Fri Oct 26, 2007 7:59 pm

So should I avoid that Joe Blow Sport?
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Unread postAuthor: DYI » Fri Oct 26, 2007 8:22 pm

Just get a decent bike pump if you want this to be cheap. The emergency tire pumps are slow, unreliable, poorly built, and prone to rapid and destructive overheating. Regulated gas from a high pressure tank would be your best bet if you have a decent budget, probably either CO2, air, or nitrogen, as helium gets expensive to buy regulators for.

As for the strength of your construction material: The calculated burst pressure for 2" schedule 40 steel pipe is around 1300 psi. Short of solid explosives, or dumping unregulated high pressure tanks into it, you will not make hardware store steel pipe fail. Considering its low quality construction methods, it is amazing how strong it is.

You really do need to use at least 200 psi or so to even make this worthwhile, unless you only plan on shooting for range. To my knowledge, no one has ever made a barrel of reasonable strength implode on a coaxial, and type M copper in those diameters should have a burst pressure of over 1000 psi, although the fittings would be less.
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Unread postAuthor: rixth » Fri Oct 26, 2007 8:50 pm

DYI wrote:As for the strength of your construction material: The calculated burst pressure for 2" schedule 40 steel pipe is around 1300 psi.


I'm unsure which schedule it is, I got it from an engineer around here. The walls are thick (maybe 3mm), so I believe it would easily take 200psi.

DYI wrote:You really do need to use at least 200 psi or so to even make this worthwhile, unless you only plan on shooting for range.


This is definitely more a range thing, though destructive power is always good. My fittings are only rated to 216psi.

What pumps do you guys use (make/model)?
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Unread postAuthor: rixth » Fri Oct 26, 2007 8:57 pm

GGDT: 160PSI with a 55 gram (2oz) projectile, range would be 497m (1600ft).

Sweeeeeeeet.
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Unread postAuthor: rixth » Fri Oct 26, 2007 9:28 pm

Oh, one more thing, how tight does a piston have to fit?

My steel pipe has a seam on the inside... =(
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Unread postAuthor: DYI » Fri Oct 26, 2007 9:42 pm

You may be able to use it, but you should use smoothe pipe if you want a working piston valve. The tighter the tolerance of the piston, the more efficient it is.

If you tell me the inner diameter and outer diameter of the pipe, I can tell you what schedule it is.

Range shots are useless on powerful guns, because you never see or find the ammo, unless it's huge and bright. I did make some range shooting ammo for my most powerful launcher though. The round is shiny black and red, 2.5 feet long, and weighs 7 pounds... It should go about 300 fps, and be relatively easy to find.
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Unread postAuthor: rixth » Fri Oct 26, 2007 10:37 pm

ID is 53mm
OD is 58mm

As for range, I live in a rural area on a 3km long straight road that has 3 houses on it, I just shoot stuff down it then go for a walk =D
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Unread postAuthor: rixth » Fri Oct 26, 2007 10:51 pm

Using this chart: http://www.dsiprocess.com/ProductsServi ... hedule.htm

It seems my pipe is only schedule 10?!

Edit: Youngstown Tube schedule 10 pipe meets the rigorous testing and certification processes of Underwriters Laboratory and Factory Mutual for steel sprinkler pipe with working pressures of 300 psi or less.

I don't know what make my pipe is, but 300psi is more than enough.
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Last edited by rixth on Fri Oct 26, 2007 10:55 pm, edited 1 time in total.

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