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Fx Impact Pellet Velocity Keeps Decreasing

Discussion in 'Technical' started by Rash, Aug 12, 2020.

  1. Rash

    Rash Member

    Messages:
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    I have Fx impact MK2 power plenum which cant hold pellet velocity.
    So, I have tuned the gun at reg pressure just below 110 bar, set valve knob to fully opened, and adjusted the hammer spring to shoot at 865 fps, shooting 5 pellets with average of 900 then reducing the valve knob until I reached 860 fps.
    Then shoot 1 mag with great accuracy but I noticed an accuracy issues starting from the second magazine so I measured the speed again and it was 800!
    However, I complete shooting without any tuning and after one more mag the speed was 777 fps. I thought it is decreasing because tank pressure was reduced as Im shooting so I refilled it to 250 bar then measured the speed and it was 770!

    Adjusted the hammer spring again to reach 865 fps but the same thing happened again!

    are Im doing something wrong or the gun need to be fixed ?

    more details:
    fx impact mk2 power plenum shooting 18.13 gr JSB pellets using fx radar chrony.

    Regards.
     
  2. Old_hand

    Old_hand Engaging Member

    Messages:
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    Location:
    lincoln, linc's
    Hammer adjuster screw works it's way out, I had exactly the same with mine. A dab (and I mean a dab) of threadlock, work the screw in and out a few times and then let it set. It'll be pretty stiff when you first turn it but, if you were very sparing with the threadlock, it'll turn ok and no more problems (until the threadlock wears out)

    If you can't get threadlock, nail varnish will work too - the important thing with either is to be sparing, like, barely touch it with the stuff kinda sparing
     
    Rash and Lordy 74 like this.
  3. Rash

    Rash Member

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    Thanks a lot for your fast reply..
    Im going to give it a try right now and will see.
    I decided to set it to 900 fps and will use a tiny amount of superglue on the hammer adjuster screw once for all :D

    by the way, what is the minimum reg prussure for fx impact mk2 with power plenum?
    Is it safe to decrease it to 85 bar for maximum shot count?

    Thanks a lot again..
     
  4. hmangphilly

    hmangphilly Keyboard Hero

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    Location:
    wimborne
    it should be safe , but you'll have to check that your reg works ok at 85 .
    you might need a lot of valve dwell to make the same power , so you could actually end up wasting a lot of air.

    best advice is try to find your gun's happy place
     
    Rash likes this.
  5. Rash

    Rash Member

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    Just finished from playing with the impact..
    I ended up setting the reg pressure to 120 bar then after 2 shots it goes to 110, I think thats normal.

    any way, now it is shooting 18.13 gr jsb at avg of 880 fps for 5 shots

    Interesting thing though that speed of cleaned pellets was much more consistent at 895 fps avg for 5 shots.
    Increment of 15 fps just because of cleaning.

    The first 5 shots were not cleaned pellets straight from the tin.
    The rest were cleaned.
    No lubrication was done to the pellets.
    All 10 shots were on one round with the same magazine.

    B3D114EA-55AF-48FE-A8D6-F8199838286E.png
     
  6. Rash

    Rash Member

    Messages:
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    Forgot to mention that after tuning the gun to 880 fps, I put tiny amount of superglue on top of the hammer adjuster screw to hold it there and then it seems that the problem is solved so far..

    Many thanks @Old_hand
     
  7. Old_hand

    Old_hand Engaging Member

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    Location:
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    You're welcome, it's good to see that it helped :thumb:
     
    Rash likes this.

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