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Need help deciding on a pump

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: jackssmirkingrevenge » Tue Jul 20, 2010 1:59 pm

ramses wrote:Wow, I feel like jack now, with all the links...


Thanks, I just realised how annoying my posts are! :roll: :D
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Unread postAuthor: ramses » Tue Jul 20, 2010 2:09 pm

jackssmirkingrevenge wrote:
ramses wrote:Wow, I feel like jack now, with all the links...


Thanks, I just realised how annoying my posts are! :roll: :D


no problem!

Oh, I just realized that you could possibly use propane gas instead of CO2. The tanks are around $2 each here, and you can use a standard compressor regulator with them, since the vapor pressure is only about 200 PSI at 90* F


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POLAND_SPUD wrote:even if there was no link I'd know it's a bot because of female name :D
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Unread postAuthor: Gun Freak » Tue Jul 20, 2010 2:10 pm

How much firing could I get off one tank?
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Unread postAuthor: ramses » Tue Jul 20, 2010 2:25 pm

hmmm... I figured that out once.

You're looking at around 8.6 cubic feet or 14850 in^3 at 80* F and atmospheric pressure. If we use an absolute pressure of 8 bar, (around 100 PSI) we can divide that volume by 8, to get 1856.25 cu in.

So divide 1856.25 cubic inches by the volume of your chamber, and you get the THEORETICAL number of shots. for example, a 2" diameter, 24" long chamber is 75.4 cu in, so you would THEORETICALLY get 24 shots.

Your chamber is significantly smaller (I hope). A .5 cu in chamber should propel a .20g airsoft BB to a respectable 380fps with a 20" barrel.

that gives you about 3712 shots, more than you have any business firing in a single game :D.
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Unread postAuthor: Gun Freak » Tue Jul 20, 2010 2:30 pm

This is for a bmmg, so how would I calculate how long it can supply air to a blowgun?
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 20, 2010 2:46 pm

Since it's for a BBMG, you'll do well to read throughthis thread to make sure you have it optimised.

If you make your design efficient, you could get the performance you want from say 50 psi instead of 100 psi, and this would automatically make your gas supply last much longer.
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Unread postAuthor: Gun Freak » Tue Jul 20, 2010 3:05 pm

Ok thanks, just read that topic, and I have most things optimized except for the barrel size, which his pretty much the most important part. The closest I can get is 7.14 mm for airsoft.
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 20, 2010 3:10 pm

Gun Freak wrote:The closest I can get is 7.14 mm for airsoft.


Hopelessly inefficient I'm afraid. Mytest had shown significant performance loss with a 11% increase in barrel diameter over projectile diameter, and in this case you have a 23% increase...
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Unread postAuthor: Gun Freak » Tue Jul 20, 2010 3:13 pm

Well, it's the closest I can get, I'm afraid.
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 20, 2010 3:25 pm

Surely you can do better.

6.5mm for example, granted there's only 30cm of it but you can easily get 2 and graft them together over a 6.5mm drill bit - besides, I'm sure there are cheaper and easier options out there if you have a look around. It will be more than worth the performance increase.
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Unread postAuthor: Gun Freak » Tue Jul 20, 2010 3:32 pm

My barrel is fixed... there is no way to get it out. I'm stuck with it unless I rebuild the entire front of my M16! I might look at a hobby store of something for a better barrel.
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Unread postAuthor: jor2daje » Tue Jul 20, 2010 3:38 pm

I dont think propane on a bbmg is a great idea because you are releasing so much air so quickly. As the liquid propane is voporized it cools and the pressure drops so you may start firing at 90 psi but after a few seconds of firing it may drop to 50 psi or so.
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Unread postAuthor: Gun Freak » Tue Jul 20, 2010 3:40 pm

I don't think I'm using propane anyways.
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 20, 2010 3:42 pm

The 6mm brass tube I linked to has an outer diameter of 7mm, so it would sleeve nicely into your existing barrel ;)
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Unread postAuthor: Gun Freak » Tue Jul 20, 2010 3:44 pm

I love you man. lol, that isn't a bad idea. I might order that... thanks a lot jack :)
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