Low joules but perfect air seal JG aug

Discussion in 'Gun Building, Modifications & Repairs' started by Coleman Kinzer, Aug 26, 2018.

  1. Coleman Kinzer

    Coleman Kinzer Member

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    The gun is a JG aug and here is a list of the factors that could be effecting bad fps -Prommy barrel with an enlarged window, bbs do slide freely through it.
    -sector gear is missing its release tooth
    -tappet plate spring was made more stiff
    -tappet plate was trimmed
    -guarder sp130 spring
    - cylinder to barrel is almost perfectly volumed for .32s
    -there is a bunch of over spin (I dont know why, gears are perfectly shimmed)
    -Lonex hop up

    Im currently getting 1.4j and it's not consistant with 280-290fps running .32s. There is a spring pressing the hop up against the gearbox aswell.
     
  2. Honeybadgerz17

    Honeybadgerz17 Well-Known Member

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    Have you checked the airseal between the nozzle and the packing/ bb
     

  3. Coleman Kinzer

    Coleman Kinzer Member

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    Yes I have, I don't know if this is a problem though but the nozzle goes deep into the lips of the bucking.
     
  4. Lefse

    Lefse Well-Known Member Supporting Member

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    Exactly what barrel and cylinder are you using? How heavy is the piston assembly?
     
  5. Coleman Kinzer

    Coleman Kinzer Member

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    Stock type 2ish 1ish looking cylinder and a prommy 285mm barrel. The piston is shs with a polycarb head, I don’t know the weight. I’m using 0.32s btw
     
  6. Corruptlol

    Corruptlol New Member

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    assuming you shot 360 on .20s , 1.4 j on .32s is a bit too much that means your barrel/cylinder ratio is not perfect.
    something is really off, i would check the orings on the nozzle and replace the pistonhead oring with a viton oring.
    i m gettin 285fps / 1.25 j - 1.3 j on .32s with a guarder m110.
    there shouldn't be overspin, with this spring.
    you definitely should replace the sector gear, thats why you get lower fps because the piston is not pushed all the way back.
    and than you should match your cylinder.
     
  7. Lefse

    Lefse Well-Known Member Supporting Member

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    You should be getting close to 2 joules with a Guarder SP130 with optimal compression, so you seem to be losing a lot of compression. Piston weight is definitely relevant, so you should weigh the piston assembly, you want a piston assembly around 25 grams for .32 gram BB's from my experience.

    How snugly does the o-ring fit in the cylinder? Do you have other BB weights to chrono with? That way you can determine if it might be under volumed or over volumed. What are you using to lubricate the cylinder?
     
  8. Corruptlol

    Corruptlol New Member

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    I m sorry but what does bb weight has to do with piston weight.
    if you tell me you shoot .32s with 25g piston assembly and a m110 i would say you will have pme same if you shoot .20s with the same setup.
    but enlighten me ;)
     
  9. Honeybadgerz17

    Honeybadgerz17 Well-Known Member

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    Think about it this way... the inertia of the piston. Rather than PME he's talking about the compression in the cylinder. A lighter piston will compress the air faster while a heavier piston will take longer to compress the same volume of air. It's basic physics. A heavier piston will create a lesser amount of kinetic energy/ velocity on the bb in the same time frame a lighter piston will.

    Work (Joules) = Force (Kinetic energy in Newton force) x D (distance) (W=FD). You get the kinetic energy by this equation KE=1/2 m(Mass) v(velocity)^2 (KE=1/2mv^2). When you have less velocity (yes more mass but velocity plays more of a factor) it creates less KE which in turn creates less joules.

    Now you cant just throw the lightest bb with the most KE behind it and expect good results. It'll either shatter, go haywire, or other bad things. This is why we find the best piston weights for certain bbs to get the most efficiency we can.

    If I missed anything lmk... I had to wake up early for PT this morning and I'm kinda tired atm...
     
  10. Lefse

    Lefse Well-Known Member Supporting Member

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    No offense, but you seem quite inexperienced with AEG upgrades. The PME "limit" isn't just affected by piston weight, it's also affected by sector gear RPM and the length of the piston stroke, it's also to a lesser extent affected by cylinder porting. A Guarder SP110 is equivalent to an M120 by the way, with optimal compression you can squeeze as much as 1.6 joules out of one.

    Piston weight does indeed affect compression efficiency. I won't pretend to understand the physics behind it, but through trial and error I've found that an excessively light piston will lower the compression efficiency. Most stock AEG's have piston assemblies that weigh around 25 grams on average, that's why stock guns often have surprisingly good compression.
     
  11. Corruptlol

    Corruptlol New Member

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    Well i heard about this but i never thought its really that relevant especially or can create such a big fps loss ( i don t think it can tbh )

    you were only talking about the piston weight, so i was only talking about this aswell.
    I know that pme is affected bei sector gear rpm and all the rest.

    Tbh i never chronod any differences between a stock lonex piston and a lightend one.
    Maybe i don t have 5k posts on this forum and only tinker on aegs for half a year but in this time i ran through around 20 aegs and atleast 300+ rhop patches.

    Anyways my main problem was that its almost irrelevant, there will never be that big of a fps loss just because the piston assembly has a weight of 5g less.
    I once had problems like this aswell and in the end it is the usual nozzle/hopup problems or some **** orings, or some parts that don t match at all.
     
  12. Honeybadgerz17

    Honeybadgerz17 Well-Known Member

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    Are you "stretching" your orings or are you using properly sized ones
     
  13. Lefse

    Lefse Well-Known Member Supporting Member

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    A 5g weight difference is 20-25% weight difference, that's definitely enough to affect the compression. I wasn't saying that OP's compression issues is caused by piston weight alone, just trying to account for all variables. You're right that one or more o-rings could be the cause, I once gained nearly 50 FPS just by replacing the piston o-ring. I'm just trying to account for all variables here because sometimes the cause is a detail one haven't even thought of.

    I didn't mean to belittle you or anything earlier, just got a bit hot headed I guess. Us old washed up techs can get a bit cranky sometimes. :D
     
  14. Corruptlol

    Corruptlol New Member

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    I never really had that much sucess with stretching so i m using the proper sized ones.

    no worries mate :)
     
  15. Honeybadgerz17

    Honeybadgerz17 Well-Known Member

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    Which size? #14 is what you should be shooting for
     
  16. Lefse

    Lefse Well-Known Member Supporting Member

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    I've given up on finding "#14" o-rings, seems to not exist in Europe. I just took a cylinder to a big hardware store, they measured the cylinder and found some o-rings that fit just snugly enough to give a nice seal.
     
    Last edited: Aug 28, 2018
  17. Coleman Kinzer

    Coleman Kinzer Member

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    I’m getting perfect compression and the piston slides freely
     
  18. Corruptlol

    Corruptlol New Member

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    So if it is not a compression issue, the cylinderhead to nozzle seal is still fine when the nozzle is all the way in the hopup, same is for nozzle to hopup seal.
    did you replaced your sector gear ?
    what did you trimmed at your tappet plate ? the fin ?
    prommy barrel with an enlarged window, you did it by yourself ? so i guess you rhoped it ?
     
  19. Coleman Kinzer

    Coleman Kinzer Member

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    sorry for late response I didnt have internet. But the nozzle does release before the piston is released. perfect seal between nozzle and bucking. I did not replace sector gear though and I may in the future but I'll have to replace the spring aswell. I cut off the fin because of feeding issues. I dont have an R hop, I have a tru hop. I needed the barrel enlarged because the nub wouldnt fit
     
  20. -Spitfire-

    -Spitfire- Well-Known Member Supporting Member

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    How did you check for airseal between nozzle and bucking, out of curiosity? Exactly how much of the fin did you cut off? I experience a drop of around 10 fps with the Truhop, iirc... and that was after switching over to a TBB, so the actual fps drop was likely closer to 20 fps. I assume you're referring to enlarging the barrel window?