Question regarding springs and stress caused

Discussion in 'Gun Building, Modifications & Repairs' started by S1kkguy, Oct 14, 2012.

  1. S1kkguy

    S1kkguy New Member

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    Hey guys got a quick question.

    Now some people don't believe me when I say so, but basically i've got an M100 spring in my aks74u and with my setup am getting fantastic compression, achieving 385-390 consistent fps. Question, is the stress to the gearbox similar to that of a higher spring giving the same fps? I'm converting my aks74u into a high ROF setup so I'd have to go for a m90 or maybe even lower if that is the case.
     
  2. Lefse

    Lefse Well-Known Member Supporting Member

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    Either your chrono is wrong, or your spring is mislabeled, I highly doubt you're getting nearly 390fps with an M100 spring. Using a weaker spring with higher ROF is also a bad idea, it will increase the risk of premature engagement of the piston.
     

  3. S1kkguy

    S1kkguy New Member

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    Chrono'd with several brands, mine is a xcortech, friend's one is a madbull. site one is also a xcortech. All show the exact same readings.

    The spring is a modify M100, I also purchased a M90 spring when I got the m100, havn't tested it yet but it is a tad bit shorter than the m100. I understand some brands shoot hotter than their ratings.

    Before I did any modifications to my gearbox it was around 330-340 with just the M100 spring and bearing spring guide. It is a cm035a. I put in a modify stainless steel cylinder head, a modify air nozzle with O ring. Then, an ASG ultimate metal hop up chamber with a KWA 2GX bucking and a modify hybrid 6.03 300mm tightbore.

    My metal hop up is the most recent upgrade, before that it was about 360-370.

    Do you reccomend I stick to this spring and use it for woodlands? Because my CQB is limited to 330fps. I'm also using a Systema A-Z motor at the moment.
     
    Last edited: Oct 14, 2012
  4. Mystery43_4

    Mystery43_4 New Member

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    Your spring is mislabeled.

    An m100 is only going to put out 330fps or so w/.20.

    It doesn't matter it the company says it's an m80, if you're getting 390 FPS with it with perfect compression, then it's an M120.
     
  5. ThompsonFTW

    ThompsonFTW New Member

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    How do spring tensioners affect this logic? Basically a spring spacer like riot as for his dsg.
     
  6. Mystery43_4

    Mystery43_4 New Member

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    It throws it off.

    Most springs are designed for standard length v2/3 GB's (and all others with the same distance between SG-CH). once you change this distance then that Spring rate is no longer in effect.

    This is why certain platforms (psg1?) have their own dedicated springs... If you throw a standard length m150 into a gb with a longer distance, you may only put out the same energy as an m120 of the proper length...
     
  7. ThompsonFTW

    ThompsonFTW New Member

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    Exactly. So,he said he was using a Latin with ballbearings. The generally will add what like %10? Which would put him at 360 on a m100.

    Do tightbore barrels get accounted into springs too?
     
  8. S1kkguy

    S1kkguy New Member

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    What I don't understand,is that with a complete stock gearbox it was giving me the 330 it was supposed to. I know this because i always chrono straight after any work I do. Unless my compression was incredibly bad, which I doubt because i re-shimmed regreased and air seal lubricated the relevant parts as soon as i bought it. I put the same spring in my mate's stock ak47 which was also a cyma to check and it was shooting about 325-335.

    Edit...Before my metal hop up unit was installed, it was the modify 6.03 TB, bearing spring guide, m100 spring, cylinder head, air nozzle and KWA 2GX bucking that achieved 350-370.
     
    Last edited: Oct 14, 2012
  9. S1kkguy

    S1kkguy New Member

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    Anyways forget the spring tension, I know what my spring is and what i'm achieving with the particular work i've done, being told what my components must be is not what I am asking for.

    Back to topic, will a spring achieving the FPS of a higher strength spring cause similar stress to my gearbox? If I need to downgrade, what is the lowest I should downgrade to? My M90 spring gives me around 350fps. However that still is above my CQB limit.

    Any negatives to m80 springs?
     
  10. CoppertopNeasg

    CoppertopNeasg New Member

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    The only negative to an m80 is that your gear box will pre-engage and if your lucky strip a piston. If your not strip gears, break piston heads, snap tappet plates or do other ungodly damage.

    You have 2 options:

    DSG
    Short Stroking

    The both do essentially the same thing which is allowing the gearbox to cycle quickly at a low fps or any fps for that matter while preventing the sector gear from engaging the piston before it has completed a full cycle.
     
    Last edited: Oct 14, 2012
  11. S1kkguy

    S1kkguy New Member

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    Thank you, from the 2 threads I have asked for advice on this forum, you have given the most constructive response! Hard to get round here, god bless ya lol
     
  12. EDI1st

    EDI1st New Member

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    To answer the original question, yes, more stress = more FPS or RPS.
    For FPS KE = 1/2 MV^2 (and then you have to calculate a bunch of fluid dynamics and lose of energy....we'll keep this simple with just that one equation.....)
    KE = the energy of BB or energy generated by the spring/piston combo.
    Higher velocity requires more energy, and it's an exponential growth (V^2)
    So.....1 Joule is about 280 FPS, but you do not get 2800 FPS with 10 Joules, you get around 1037fps assuming there's no air resistance/friction/lose of energy.

    While the piston is moving forward, energy is transferred onto the BB through air.
    But when that piston stops by the cylinder head, the whole force is released onto the gear box.


    RPS part is a bit more complicated....
    But uh...if you want to keep it simple.....it's like rocking a boat side to side, if you rock it fast and hard enough, eventually it'll tip over...(that really isn't a good terminology but close enough.....)
     
  13. S1kkguy

    S1kkguy New Member

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    knowledge, i love it! :D

    But when the fps is increased through an air seal upgrade, and the FPS achieved is that similar of a spring the next grade up, is it delivering similar stress levels, to the the higher grade spring?

    My assumption would be yes, because of the force caused by the piston delivering a greater amount of air?
     
    Last edited: Oct 16, 2012
  14. EDI1st

    EDI1st New Member

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    Well air is just the medium that the energy is transferred from the spring/piston to the BBs.
    When air seal is improved, the increase of FPS is due to removing the "loss of energy" from the system.
    It does NOT add more stress to the system. (Other than more air pressure.)

    It's like the engine of cars, energy can be lost through leak, sound and heat.
    Take the Bugatti Veyron for example, the engines actually produce more than 3000HP but all of those are lost through heat and sound.
     
  15. S1kkguy

    S1kkguy New Member

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    Makes sense, it was that increase in air pressure I was referring to as a possible stress increase variable.

    Thanks for the responses, I got the answers I wanted from this thread.