Downgrading P90 spring

Discussion in 'Gun Building, Modifications & Repairs' started by MicroMasjien, Oct 26, 2021.

  1. MicroMasjien

    MicroMasjien New Member

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    Hi!

    I need to downgrade my P90 fps, I'm getting close to 400fps, but need to be at 330fps for indoors. I bought an Evike M85 spring, thinking this will surely get me below 330fps, but I'm still at 350fps. When comparing the M85 spring, the length is much longer than the stock spring, it's more than an inch longer. My stock spring is about 5.5 inches. It's actually really difficult to squeeze it into the gearbox, much more difficult than the stock spring that's shorter but stiffer.

    So, a few questions:

    1) I don't think a V6 gearbox requires a different type of spring, right?
    2) Are there springs available that's shorter and would be easier to install?
    3) M85 is the lowest spring you get, would a spring from another manufacturer get me lower?
    4) Other than downgrading my compression parts, which I really really don't want to do, is there something else I can do. E.g. I read that someone suggested cutting out a couple of coils from the spring, but that will surely damage the piston head, right?

    Thanks!
     
  2. aotsukisho

    aotsukisho Well-Known Member

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    Prometheus MS90SP, if not then Guarder SP90. You might need to remove the bearings on the piston head and spring guide, if present.

    M100 is the M-rated spring you need, given that 100m/s = 328fps. SP-rated springs are target velocity for 0.25g bbs instead of 0.20g

    Cutting the spring is fine in small amounts but obviously irreversible.

    Never 'downgrade' compression parts, because you may introduce FPS inconsistencies and thus accuracy suffers
     
    JHat likes this.

  3. Ben3721

    Ben3721 Well-Known Member

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    Be aware when running extremely weak springs that you may have PME if you use a high voltage battery such as a 3 cell lipo. Just a heads up.

    Spring length doesn't really tell much about the spring. A true M85 spring should be very easy to install compared to a m120 spring. You can clip the spring if you need to lower your fps. Make sure the clipped end goes into the piston.
     
    JHat likes this.
  4. Airsoft_Leviathan

    Airsoft_Leviathan New Member

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    Well, for one thing the Evike brand springs are all made of super soft material. They start out shooting pretty hot and then have to settle to a lower power. This is because they tend to be made of lower quality metal. If you fire 500 or so rounds on that spring, you probably can get it below field limits. Personally it’s been a nightmare to find good brands for springs that don’t have to settle and are reliable. In an industry with no standards, QC and reliability go out the window. One brand that was considered “good” one year is considered “terrible” the next. Good luck with your build and happy airsofting!
     
  5. MicroMasjien

    MicroMasjien New Member

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    Interesting point. The spring is brand new. I wonder if I should perhaps leave the gun pre-cocked for a day or two to let the spring settle in.
     
  6. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

    8,357
    4,726
    Minneapolis
    Leave it cocked for 2 weeks.

    If it's an Evike House Brand item. It is definitely a soft spring and it has not settled to the designated rating yet. If it's hard to install you may have received the "wrong" spring. It happens more frequently than not...sadly...
     
  7. MicroMasjien

    MicroMasjien New Member

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    After about a week of pre-cocking, it's gone down from 350 to 340, so getting there. I'll report back in another week.
     
    JHat likes this.
  8. JHat

    JHat Active Member

    525
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    Elk Grove
  9. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

    8,357
    4,726
    Minneapolis
    That would be a sub 300fps spring...or near 300.
     
  10. aotsukisho

    aotsukisho Well-Known Member

    790
    439
    Correct, 85m/s with 0.25g = 279fps which translates to 312fps with 0.20g (0.9J) under whatever test conditions are used by Guarder (3/4 ported cylinder, 363mm M4 barrel?)
     
  11. MicroMasjien

    MicroMasjien New Member

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    Another update, after two weeks of pre-cocking, I'm still at 340fps. I guess I'll cut out a couple of spring coils.
     
  12. MicroMasjien

    MicroMasjien New Member

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    Final update, after shortening the spring by a couple of coils, I'm now at 320fps. Rather 10 under the limit and allowed to play, vs. 10 over the limit and not allowed to play :)
     
    aotsukisho likes this.