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    FPS and Barrel Length

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    Timothy T
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    FPS and Barrel Length

    Post  Timothy T on Sat Mar 13, 2010 3:28 am

    Hey, I've searched high and low for this but can't find it.

    I'm looking for some kinda of graph showing the relationship between barrel length and fps. Or failling that, something more technical than the standard 'It barely does anything/it does quite a bit'.


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    Elle_Brock
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    Re: FPS and Barrel Length

    Post  Elle_Brock on Wed Mar 24, 2010 1:48 am

    swear I saw something along those lines not to long ago trying to think where I saw it darn it.
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    Taelon
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    Re: FPS and Barrel Length

    Post  Taelon on Sun May 02, 2010 6:58 am

    Last time I checked it has little effect on AEG's but does wonders on a GBB, same for a tighter barrel. Also know I havent gone out of my way to check this.


    LOL... googling "furry"... thats a funny one, always a good reaction to that (no it wasnt me that told him to do it)
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    Mikey
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    Re: FPS and Barrel Length

    Post  Mikey on Mon May 03, 2010 6:21 am

    I have some data and some graphs of my own making, but its so incomplete its unfair to draw any conlcusive info from it, as there are many other factors to take into account such as cylinder size and porting, spring tension, BB weight.
    It does however point to a fairly good rule of sorts:

    FPS IS directly proportional to barrel length AND spring power UNTIL the length of barrel matches the porting of the cylinder, at which point any further increase in barrel length has NO additional effect.

    A tightbore makes a little difference to FPS

    A significantly overlong barrel will noticbly reduce FPS.

    Lighter BB's gain more from a longer barrel than heavy ones.

    For what its worth, heres the results from my M4, which was the most consistent gun tested.... draw your own conclusions Smile

    gun barel brand length 0.12 0.2 0.25
    M4 MP5k 110mm Galaxy 110 250 230 220
    M4 std cqb 273mm G&P 273 412 349 313
    M4 Tightbore 404mm Systema 404 479 368 345
    M4 AK47 455mm JG 455 470 367 339
    M4 G36 509mm SRC 509 479 368 343
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    Timothy T
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    Re: FPS and Barrel Length

    Post  Timothy T on Mon May 03, 2010 7:09 am

    Could it be arranged into a bmp file or something? I am having trouble reading it.


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    Re: FPS and Barrel Length

    Post  Mikey on Mon May 03, 2010 7:14 am

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    Timothy T
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    Re: FPS and Barrel Length

    Post  Timothy T on Mon May 03, 2010 7:40 am

    So the bottom row is BB wieght, the side row is FPS and each colour line is a barrel length. Hmm, I was surprised at how much the FPS drops with the BB wieght. Doesn't drop much with the lower FPS barrel so I guess heavier bullets are better for lower power guns? Very interesting how there was little difference between the 404mm barrel and the 509mm barrel.

    But, like you said, not much tests. Which makes this, weak, on the inductive reasoning.

    Not be all negative but this doesn't help me with my EBB problem, *sigh*.


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    Re: FPS and Barrel Length

    Post  Mikey on Mon May 03, 2010 8:02 am

    I also tested the mp5k with different barrels and the g36 - the results were quite different. Try and compare only the shape of the lines, not the actual fps measurement to get an idea of how porting interacts with barrel length.
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    Re: FPS and Barrel Length

    Post  Mikey on Mon May 03, 2010 8:05 am

    I believe that with some air seal work and a bigger spring the g36 would see consistent benfit from a longer barrel. The MP5k is doomed with its much smaller lungs.

    (edit) The G36 has no port, the M4 has a modest port and the MP5k has serious porting. Porting effective reduces the size of the cylinder
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    Timothy T
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    Re: FPS and Barrel Length

    Post  Timothy T on Mon May 03, 2010 9:54 am

    So how does a longer barrel negativly effect the FPS? I would have thought it would just level out and stay there. Maybe it's something to do with the seal. I dunno.

    Is porting the sealness of the gun?


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    pota
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    Re: FPS and Barrel Length

    Post  pota on Mon May 03, 2010 9:02 pm

    i do agree with miky i think the extened barral could effecively say reppale the pellet in a sence of speed against no barrer....
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    Re: FPS and Barrel Length

    Post  nz3rdsqr on Wed May 05, 2010 6:44 am

    the way it would reduce the fps is once all the air that fits in the piston is in the barrel then the bb will act as its own piston creating a vacume in the space behind it this effectivly sucks the bb back causing the drop in fps. i hope you can undersatnd this if not tell me and i will try to simplyfy it.
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    Timothy T
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    Re: FPS and Barrel Length

    Post  Timothy T on Wed May 05, 2010 6:58 am

    Nope Ray, the piston only has so much power.


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    Re: FPS and Barrel Length

    Post  Hazard "The Executioner" on Wed May 05, 2010 8:28 am

    time to upgrade ye olde' start menu aye mikey?
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    Mikey
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    Re: FPS and Barrel Length

    Post  Mikey on Wed May 05, 2010 10:00 am

    So..... how bout that resistance to change....
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    Re: FPS and Barrel Length

    Post  Hazard "The Executioner" on Wed May 05, 2010 10:05 am

    just wait until you see mah alienware gears Very Happy

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