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help with air champer volume

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help with air champer volume

Unread postAuthor: far_cry » Tue Aug 26, 2008 6:05 pm

i build an air rifle with 8mm barrel and a chamber with 320 cm3 volume
and i build an air pump that can pump a 400 psi
what the best volume (in cm3) to shot one shot at one full comprised air chamber ?
i ask that question because
1 at took a loot of time to fill the chamber
2 i afraid 'when i fill that chamber and shot an air pressure will stay and go out side after the ammo no longer in the barrel such i waste !!!
thank you
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Unread postAuthor: psycix » Tue Aug 26, 2008 6:25 pm

With such a high pressure and a large chamber, you should use a long barrel for the best performance.
If you want to pump less, make the chamber smaller. Do not drop pressure.
It is quite a waste, but this waste does generate the bang.
If you want to waste less, use longer barrels, and possibly smaller chambers.
Again, dont drop pressure, drop the chamber size if you want to pump/waste less. Its better to have a chamber half the size with the same pressure then a chamber with half the pressure and the same size.
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Unread postAuthor: far_cry » Tue Aug 26, 2008 8:03 pm

thank you psycix
so i will make a smaller chamber about 80 cm3
with 400 psi it is enough ?
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Unread postAuthor: Gippeto » Tue Aug 26, 2008 11:31 pm

Opinions vary on this issue. :)

I tend to use less than 1:1 ratios for my launchers. Particularly the high pressure ones.

If you were to use a 100cm barrel that was 8mm id. , your barrel volume would be approximately 50.27cm3 . I would suggest that a chamber of LESS than 50 cm3 would be just fine.

My copper gun (400psi), has a barrel which is approximately 14mm id and 91.4cm in length. This works out to a barrel volume of 140.8cm3

The chamber is approximately, 2.06cm id and 35.56 cm in length, for a chamber volume of 118.4 cm3.

My chamber is roughly 84% the volume of my barrel, and I am very pleased with the performance.

Have you downloaded GGDT yet?
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Unread postAuthor: far_cry » Wed Aug 27, 2008 5:29 am

thank you gippeto you rock :wav:
youre answers are full of expertise
and 400 psi is high pressure ? not enough to me, i wanna get 200 bar

and what is GGDT i am new in the busines 8) 8)
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Unread postAuthor: POLAND_SPUD » Wed Aug 27, 2008 5:52 am

i am new in the busines
and
and 400 psi is high pressure ? not enough to me, i wanna get 200 bar
no offence but it's not good that these two sentences are together in one post...

400psi can be very dangerous if something goes wrong... 200bar is almost ten times that......

if you have access to machinery and knowledge like gippetto or larda you can give it a try... but otherwise you put your life at risk
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Last edited by POLAND_SPUD on Wed Aug 27, 2008 1:39 pm, edited 2 times in total.
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Unread postAuthor: far_cry » Wed Aug 27, 2008 6:24 am

i guess i am not :twisted: :twisted: :twisted: :twisted: :twisted:
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Unread postAuthor: Gippeto » Wed Aug 27, 2008 9:07 am

GGDT (Gas Gun Design Tool) is a wonderful program that will enable you to build VIRTUAL launchers and test their performance.

Design it, model it and change it, all before you spend money building the real thing. :)

Download it here;

http://www.thehalls-in-bfe.com/GGDT

Just follow the instructions to set it up.
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Unread postAuthor: far_cry » Thu Aug 28, 2008 7:08 am

VIRTUAL data thate software give me (ggdt) is not reliable 100%
because what is on the paper no way can be in the real world
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Unread postAuthor: jimmy101 » Thu Aug 28, 2008 12:56 pm

far_cry wrote:VIRTUAL data thate software give me (ggdt) is not reliable 100%
because what is on the paper no way can be in the real world

(If I understand what you said correctly ...) GGDT is pretty darn good. If you can adequately describe the valve then the GGDT results will generally be more than accurate enough. Often the difference beteeen a GGDT prediction and the actual performance is less than the shot to shot variability of the particular gun + ammo combination.

Besides, the real power of GGDT is not that it can accurately model a gun (which it can), it is that it can accurately model the affect of changes to a given gun design. Questions like "how much will the performance drop if I cut the chamber volume in half?" are perfect for GGDT.
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Unread postAuthor: jackssmirkingrevenge » Thu Aug 28, 2008 1:20 pm

have a look here, for the same quantity of air, smaller volume and higher pressure yields significantly more power ;)
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Unread postAuthor: far_cry » Thu Aug 28, 2008 1:40 pm

thanks all you are very helpful guys
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