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Deciding barrel length

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Deciding barrel length

Unread postAuthor: farcticox1 » Sun Sep 21, 2014 3:23 pm

Max Velocity: (0.20g BB @ 120 PSI)
275mm Inner Barrel: 380 FPS
380mm Inner Barrel: 405 FPS
509mm Inner Barrel: 435 FPS
*FPS listed is approximate. FPS will increase as barrel length increases

Image

Got the above figures off a Airsoft site, was planning to upgrade my compressor to a 200psi, and go to airsoft ammo instead of steel BBs, my barrel length is now 760mm/30",6.01mm ID, does that seem a bit long ? There must be a point where extra length has no or negative effect on FPS.

Any body seen/done any chrono tests on barrel length v FPS v pressure ? :idea:

Thanks
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farcticox1
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Re: Deciding barrel length

Unread postAuthor: mark.f » Sun Sep 21, 2014 6:36 pm

Such a test would be worthless given the variety of ammunition used, along with different gases (CO2, air, etc.).

Your best resource here is GGDT or another 1D gun simulator, so you can play with your setup before building.

But yes, barrel length has a diminishing return given a fixed pressure/chamber volume/projectile.
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Re: Deciding barrel length

Unread postAuthor: farcticox1 » Mon Sep 22, 2014 1:02 pm

:idea: Think I'll have to get myself a chrono
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Re: Deciding barrel length

Unread postAuthor: Technician1002 » Mon Sep 22, 2014 1:48 pm

I have done some barrel length vs pressure testing on a much larger bore t shirt launcher. There is a point of diminsihed returns even to the point of negative returns.

If you would like to see the test, this covers it. This proceedure will not work on metal launchers unfortunatly.

https://inteltrailblazerschallenge.wikispaces.com/Barrel+length+trim+method

This testing saved a lot of cutting barrels as we started long for the pressure and could tell in the barrel where diminished returns were. When finished we were able to shoot a hole in a piece of wall to wall carpet draped over a sawhorse using only a rolled up t shirt.

Indication of no return is where the projectile travels serveral feet in a barrel with no appreciable increase in speed as indicated by this test shot. The below is the last of 10 sensors spaced a foot apart on a barrel.

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Re: Deciding barrel length

Unread postAuthor: farcticox1 » Mon Sep 22, 2014 4:47 pm

Like Myth Buster when they fired a pingpong ball above the speed of sound 8)
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