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5/16th or 9/32?

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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5/16th or 9/32?

Unread postAuthor: Mitchza89 » Mon Sep 03, 2007 1:52 am

G'day....me again.. I've been told 5/16 and 9/32 is perfect for BB's

But aren't they the same or does one fit bb's better then the other?
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Unread postAuthor: jrrdw » Mon Sep 03, 2007 4:53 am

No not the same, 5/16ths is to big for .177 caliber BB's.
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Unread postAuthor: Mitchza89 » Mon Sep 03, 2007 4:54 am

Thanks alot. so for 6mm bb's, 9/32 all the way.
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Unread postAuthor: jrrdw » Mon Sep 03, 2007 4:59 am

No, 6MM are Airsoft plastic pellets. The 5/16ths would fit them better.
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Unread postAuthor: Mitchza89 » Mon Sep 03, 2007 5:27 am

Ah yep fair enough. Well I intend to shoot the yellow 6mm air soft bb's and 6mm lead fishing sinkers so yeah, 5/16 would be better then. Thanks for that mate.

Any clue what the ID difference is between the 2?
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Unread postAuthor: jackssmirkingrevenge » Mon Sep 03, 2007 6:30 am

Do you have a hobby/RC/model shop near by? If so you should pay a visit, they should stock lengths of brass tubing with an I/D of 6mm.
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Unread postAuthor: Mitchza89 » Mon Sep 03, 2007 6:34 am

Yeah I've gotten some 9/32 aluminium tubing there before. I stuck it through 2 corks and sleeved it into my marble gun by brute force. It worked perfect at 110psi.....So I put it up to 120psi and it blew out like a harpoon and completely bent n compacted.

It was good tube but it was just really flimsy. I bent it many times before it harpooned just be accidently knocking it against the wall.

So I'm gonna try some brass. I reckon it'll be alot stronger.
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Unread postAuthor: jackssmirkingrevenge » Mon Sep 03, 2007 6:37 am

I only use brass tubing in my high pressure BB launchers, I/D 6mm with a wall thickness of 0.5mm, I suppose you could sleeve it for extra strength but I find it adequate for my purposes.
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Unread postAuthor: Mitchza89 » Mon Sep 03, 2007 6:40 am

Yeah that sounds good. What performance where ya getting with your bb gun at what psi mate? With the 6mm lead balls I plan to shoot, ggdt calculated about 600fps. I dont know if thats particularly good...what do you think?
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Unread postAuthor: jrrdw » Mon Sep 03, 2007 6:48 am

600' per second is cranking them out there pretty good. Be carefull with that lead shot, harmfull on more then 1 level.
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Unread postAuthor: Mitchza89 » Mon Sep 03, 2007 6:50 am

Yeah thats it. It weighs as much as a marble and is travelling at about the same as a marble, with the size of it.....means for ALOT of penetrating power.
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Unread postAuthor: jackssmirkingrevenge » Mon Sep 03, 2007 6:50 am

The best velocity I ever got at 400 psi was 1012 fps for a 0.12 gram airsoft BB. With lead pellets (1 gram) at 400 psi and a 36 inch barrel I got around 650 feet per second. A 6mm lead ball will weigh about the same so you should have similar results - penetration at that velocity is quite impressive, you'll have almost double the muzzle energy of your average pellet gun.
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Unread postAuthor: Mitchza89 » Mon Sep 03, 2007 6:54 am

Damn thats some great speed. Must be like a nailgun, I'm really looking forward to getting this built. Do you have any pictures of the gun itself?
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Unread postAuthor: jackssmirkingrevenge » Mon Sep 03, 2007 7:05 am

Mitchza89 wrote:Do you have any pictures of the gun itself?


here it is, this is the breech end:

Image

This is what the internals look like:

Image

However it became apparent that for the barrel length, I had made the chamber too small, so I doubled the volume like so:

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Unread postAuthor: Mitchza89 » Mon Sep 03, 2007 7:14 am

Wow. Thats really well made mate. Would have taken a while not to mention alot of planning to build.

The one I'm building will be like a shotgun. It will be like a Coax in a sense because the chamber will be around the barrel but the barrel extends back into a 1/2 brass tee to make a Tee valve. I'm doing it this way so I can attatch the pump straight to the chamber so it's much as much of a conventional bb gun as it can possibly get.
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Coax BB Gun.jpg
Its a bit out of proportion but the chamber is 1/2in that goes into 1/2in T, that goes into a 15mmx6mm nipple, straight into a 6mm tee.
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