Featured need to lower fps on Cybergun licensed p90 (question)

Discussion in 'Gun Building, Modifications & Repairs' started by diddly dee, Jan 13, 2022.

  1. diddly dee

    diddly dee New Member

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    I recently bought the cybergun FN herstal p90. Shoots a little too much for my fields and am looking for a way to get fps under 300. looked into an M80 spring but wasnt sure if that would work because i dont know much about the parts.
    couldnt find a ton of info on the parts but i do know it has a V6 gearbox (full metal fully upgradeable), a long type motor, and a 290mm lenght inner barrel
     
    Last edited: Jan 13, 2022
  2. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    M80 does not exist.

    If that did exist it would render your AEG with a pitiful ROF to prevent PME.

    The simplest way to cut speed with your AEG is to reduce barrel length. Reducing that barrel to under 190mm should get you close to your desired FPS of 300..

    CYB also uses low grade springs. The tension will soften over a short period too, especially if left in a compressed stated after use in FA mode.
     
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  3. Ben3721

    Ben3721 Well-Known Member

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    I worked on one of these guns the other day, it was incredibly easy to get the gearbox out and to open it. You'll need to clip a soft spring to get your fps goal, but keep the rps low so you don't pme the piston.

    The internals of that aeg aren't too bad at least.
     
  4. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    P90 Mechbox are as easy as AUG mechboxes to get out.
     
  5. diddly dee

    diddly dee New Member

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    reducing the inner barrel would make it stop inside the aeg, this is alright?
     
  6. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Having the inner barrel be shorter than the outer barrel is not an issue if it's aligned correctly.

    G&G ARP 9 is such an AEG.

    M120 class spring to allow high rps under a 3S LIPO to prevent PME.

    Yet stock barrel is ~150mm.
     
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  7. Graybeard

    Graybeard Active Member

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  8. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Pre-Mature Engagement - Specifically when the sector gear is coming back around to try and pick up the piston to wind it back before the piston has finished it stroke. Most common when you run an AEG outside of it's spec in high ROF without doing the proper system prep.

    Of if you use a "weak" spring and your AEG your AEG is running under normal speeds...thus the issue with a M80 spring.

    A PME'd piston.

    [​IMG]
     
  9. diddly dee

    diddly dee New Member

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    any reccomended barrels? also would replacing the barrel cause PME or other problems if done correctly
     
  10. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Barrel changes have no bearing on mechbox function. This is how you can lower FPS to "prevent" PME inside the mechbox.

    Many people are going Maple Leaf Hybrid. For this kind of setup...
     
  11. Ben3721

    Ben3721 Well-Known Member

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    I don't thing you can install a much shorter barrel in this p90, maybe a inch or two but that's about it.
     
  12. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Oh that's right...P90, duh.

    What is the fps your getting now with .20g?
     
  13. diddly dee

    diddly dee New Member

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    about 400 with .20
     
  14. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    If you have a cylinder with a hole in it...Type 2, reverse it. That should knock you down to the high 280s...if not middle 200's. If not a Type 3 cylinder will reduce air pressure...thus dropping your fps also.
     
  15. Graybeard

    Graybeard Active Member

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    He said it has a 290 mm inner…..what problems would there be with going shorter?
     
  16. diddly dee

    diddly dee New Member

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    what do you mean by reverse the cylinder? Not sure if this helps but I have a V6 gearbox which I may have forgot to mention.
     
    Last edited: Jan 14, 2022 at 1:59 AM
  17. diddly dee

    diddly dee New Member

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    Forgot to say that the chronograph for under 300fps is done with .25's
     
  18. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    P90 all have V6 mechboxes, but that is not an issue.

    Reverse the cylinder means, you put it in backwards.

    upload_2022-1-14_9-1-15.png

    ^Type 3 Cylinder, based on hole position the point, points to the front. If you reverse it. The cylinder has less air capacity, thus your pressure wave will be smaller and your bb slows down.

    This isn't a large drop that you need. Reversing your stock cylinder may give you this performance decrease or swapping down to a 190mm barrel will definitely put you near your speed limit and you won't need to modify your mechbox.
     
  19. diddly dee

    diddly dee New Member

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    thanks for all your help, it really helped
     
  20. diddly dee

    diddly dee New Member

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    just tried putting the cylinder in backwards and the bb's dropped about 2 inches from the barrel if they even got to the barrel. Also could have been error putting it back together, would reversing the cylinder do this or do i have another issue i just made. (edit) I made an issue
     
    Last edited: Jan 15, 2022 at 3:37 PM