What Barrel Length goes with what bb weight in an AEG?

Discussion in 'Gun Building, Modifications & Repairs' started by 1tonne, Aug 12, 2018.

  1. the airsoft scientist

    the airsoft scientist Active Member

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    Oh okay thanks, thought it would be something like that
     
  2. BOA_SP3CT3R

    BOA_SP3CT3R Moderator Staff Member Moderator Supporting Member

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    You could use a POM half rack piston like a JG Black 7t, Prometheus Hard, System SuperCore, Action Army/Magic Box POM, etc. The lower friction of the polyoxymethylene/polyacetal teeth *may* help with noise and efficiency, and have excellent durability. Plus there's a ton of support behind the steel rack.

    Having perfect Angle of Engagement, shimming, gear+piston meshing, motor alignment and axle support can greatly reduce noise. I've found that some bushings such as SHS have too much axle play and so the gears can wobble a bit and be loud even with good shimming. The ZCi Enhanced or FLT bushings have less play and decrease noise. I think you were using bearings though so that shouldn't be an issue.

    A combination of low ratio gears(10-13:1) and a high TPA motor(22-32, anything above is a bit overkill) works well for decreasing cycle time. Pre-cocking can help a lot too.

    One thing tho...too light of a piston can, as you probably know, decrease compression efficiency and power output. 11g is super light.
     
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  3. 1tonne

    1tonne Well-Known Member

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    Thanks Boa for the info.

    I will try some 10:1's or something like that and will look for a motor between 22-32 TPA.

    I understand how the light piston can decrease the power output in regards to Joule Creep but how does it decrease compression efficiency? I would have thought that a light piston would mean instant acceleration and therefore the O-ring would expand a lot quicker meaning more instant compression and since it is so light it would mean that the spring could expand a lot faster giving higher fps.
     
  4. 1tonne

    1tonne Well-Known Member

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    Where do I get 10:1 gears from? Can't find them anywhere apart from Seigetek ones that cost the earth.
     
    Last edited: Sep 9, 2018
  5. Airborne101

    Airborne101 Well-Known Member

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    Seigetek are the only ones that make them. I think the next lowest ratio are 12:1 by SHS.
     
  6. skipper363

    skipper363 Active Member

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    What weight is optimized for gbb pistols?
     
  7. 1tonne

    1tonne Well-Known Member

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    That depends on the amount of gas the pistol is letting out, what pressure it is coming out at and also the barrel length. This can vary a lot so I can't give you an answer on that one. Cheers
     
  8. Evan J Johnston

    Evan J Johnston Member

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    @1tonne Any chance you'd divulge the rest of your data and conclusions from these experiments? This information seems to be sinking deeper into the interwebs.
     
  9. skipper363

    skipper363 Active Member

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    How deep did you have to go to find this thread man....
     
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  10. 1tonne

    1tonne Well-Known Member

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    These suggested barrel lengths are done with a full cylinder. They are only a guideline but it is what I use.
    You can use the ratios for other barrel lengths

    BB weight-----Barrel Length-- Barrel Volume----- Ratio
    0.2gm------------435mm---------12423mm3------2.17:1
    0.23gm----------430mm---------12280mm3-------2.19:1
    0.25gm----------425mm---------12137mm3-------2.22:1
    0.28gm----------420mm---------11994mm3-------2.24:1
    0.30gm----------415mm---------11851mm3-------2.27:1
    0.32gm----------400mm---------11423mm3-------2.36:1
    0.36gm----------380mm---------10852mm3-------2.48:1
    0.40gm----------355mm---------10138mm3-------2.65:1
    0.43gm----------345mm----------9852mm3-------2.73:1
    0.45gm----------335mm----------9567mm3-------2.81:1
     
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  11. Evan J Johnston

    Evan J Johnston Member

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    Not crazy deep honestly. Used the forum search function for "cylinder volume ratio" I believe and just opened up anything that seemed relevant. Found a thread where someone linked this one.
    Yeah I screenshotted this from the OP haha. So is that a no-go on divulging the raw data?
     
  12. 1tonne

    1tonne Well-Known Member

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    It is a no go. Mainly because it shows how to joule creep an AEG rifle to ridiculous amounts. I had just shy of 300% extra energy using the heavy bb over the 0.2gm. So incredibly dangerous.
    I do not want our sport wrecked.
     
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  13. Evan J Johnston

    Evan J Johnston Member

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    With great power comes great responsibility. Was there really such minimal accuracy loss with the joule creeping?
     
  14. Guges Mk3

    Guges Mk3 Well-Known Member Supporting Member Lifetime Supporter

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    Law of Inertia says - Yes.
     
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