Is it possible to tweak spring FPS output?

Discussion in 'Gun Building, Modifications & Repairs' started by Dwosky, Feb 27, 2018.

  1. Dwosky

    Dwosky Member

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    For my ICS I've purchased two different Guarder springs, one SP120 and one SP130, since I wasn't sure which one would let me near the 450 FPS limit I have in my field. The problem is that neither leave me there. The SP120 gives 415 FPS and the SP130 470 FPS.

    Talking with the store clerk he told me something like adding shims or something like that to the SP120 in order to reduce the space it has to compress and thus gain some FPS in the process. Has anyone do or find anything regarding this issue?

    I could also cut the SP130 a little, but I'm no expert and I'm not sure how much should I take. Also I believe the end result might not be as good as the whole thing.
     
  2. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Do you have bearings on your AEG Piston head or Spring guide? If you do...remove them. Not needed if you have a sliding spacer on the spring guide...bearings is a solution for a problem that does not exist any more. If you have both it will definitely drop you under 450 on your M130.
     

  3. Peeque

    Peeque Well-Known Member Supporting Member

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    I've had to cut springs a couple times to get under the fps limit. I would do one coil at a time until you get to where you want. Make sure you cut on the end that goes in the piston and then bend where you cut so that it's flat like it was, otherwise it can dig into your piston head and cause all kinds of fun problems. If you have spacers I would do that instead so you don't have to cut up a spring.
     
  4. BOA_SP3CT3R

    BOA_SP3CT3R Moderator Staff Member Moderator Supporting Member

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    How's your air seal? I'd think you'd get more than 415 on an SP120(~m130). Improve air seal, add spacers, maybe piston weight, and you'll get more fps.
     
  5. Uller

    Uller Well-Known Member

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    Simple.If your only 20 fps over your limit simply leave your SP130 spring compressed in your gun for a day.Decompress it,then test.If it's still too high compress the spring and wait another day,then test again.Eventually you should get it pretty close.Boa is correct,you should be getting pretty close to your goal with the SP120.Go down to an auto parts store and pick up a tube of this;https://m.grainger.com/mobile/produ...0014!&ef_id=WBBjSgAAAC1QjSP3:20180228030851:s I started using this yrs ago when I used to build engines,works great on CH to cylinder unions,to seal buckings to barrels.If you can swing it I highly recommend Speed Airsoft PH's.You will get absolute compression with those.Before investing in one pull your cylinder assembly out,remove your air nozzle,and compression test your cylinder.Do this after applying the anaerobic.You do it like that you have eliminated one point of compression loss.When applying the anaerobic,only smear a film of the material on the Orings of your CH,and on the bottom of your barrel,sides,and around the muzzle end of the spacer window.
     
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  6. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    However, if he has a High quality spring it will not compress down much. Guarder are pretty decent...they may lose about 3% after 2 weeks of compression
     
  7. Dwosky

    Dwosky Member

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    Its kinda hard to go for the compression stress option, since I believe I could also affect the gear pinions (as they will be stressed out).

    I've checked the air seal and between the cylinder head and the nozzle its a joke, with the nozzle one I can push the piston all the way down without much resistance. Without the nozzle, I need to push the piston way harder. BTW, without the nozzle I'm able to completely push the piston in (with force) having my thumb pressed on the cylinder head exit hole. Should I be able to do that? I mean, I don't remember if the piston has to do resistance once you push it or shouldn't move a bit in order to evaluate the air seal on that part.

    Regarding the nozzle, since this is ICS and has a weird nozzle/cylinder head, I'm not sure if I can seal that somehow. Any ideas?
     
  8. Lefse

    Lefse Well-Known Member Supporting Member

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    Nozzle to bucking seal is more critical, nozzle to cylinder head seal actually has little effect on compression efficiency and consistency, unless it's a major leak. I've gotten within -+2 FPS deviation with nozzles that had a significant leak, that's consistent enough for most applications really. How snug is the o-ring inside the cylinder and how much does the piston weigh?

    It's odd that you seem to have better compression efficiency with the SP130 than with the SP120. The SP120 should give 430 at least with good air seal and optimal compression efficiency, might get close to 440 if everything is optimal.
     
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  9. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Hallelujah another brother of the true physical faith!

    Don't buy and use an o-ring nozzle unless it is perfectly "light" on the cylinder nozzle tube, any resistance can cause issues and there is no major benefit due to pressure flow patterns.
     
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  10. Dwosky

    Dwosky Member

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    I've checked the nozzle to bucking seal and it seems to be correct, in fact due to the ICS hop up unit design the nozzle its way inside it.

    I've checked the hop up & barrel for leaks and I wasn't able to successfully blow air once the end of the barrel and the feeding tube where covered.

    I also believe it odd to be such difference between the SP120 and the SP130, but the vendor told me it was correct.
     

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  11. Lefse

    Lefse Well-Known Member Supporting Member

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    415 FPS with a Guarder SP120 is very low considering you can get up to 410 with an SP110 with optimal compression. Vendors doesn't always know what they're talking about, a local vendor claimed that the current world record for ROF is 32 RPS with a moped battery...

    It is possible that the SP120 is actually an SP110 spring that has snuck it's way into an SP120 packaging or that it has a manufacturing flaw.
     
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  12. BOA_SP3CT3R

    BOA_SP3CT3R Moderator Staff Member Moderator Supporting Member

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    I remember reading that in one of your posts somewhere:p
     
  13. Lefse

    Lefse Well-Known Member Supporting Member

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    I don't even use SHS/DA springs anymore, I only use Guarder now, and a Systema spring in one of my AK's.
    Yeah, to put things into perspective, that store chain is the biggest distributor of Cyberfu-, err Cybergun products in Norway.
     
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  14. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    CYB...I knew them well and they are a bunch of arrogant idiots...
     
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  15. Dwosky

    Dwosky Member

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    Ok, in the end I was able to do a cheap mod with a 1 cent coin :)

    I've placed the coin in the base of the inner cylinder in the piston, so it sits over the screw to fix body & head (of the piston). I've lost the ball bearing from it, but I've been able to reduce in 1-2cm the spring space without messing with the AoE.

    In the end I've gained 10-15 FPS, the replica now sits over 428-430FPS, which is more acceptable from my point of view. I don't have so much difference over the limit (450), but I have some safe value in case the field chrono marks a higher value than my chrono.
     
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  16. BOA_SP3CT3R

    BOA_SP3CT3R Moderator Staff Member Moderator Supporting Member

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    Out of curiosity, what is the barrel length and piston weight(or just the piston+PH brand)?
    I had a thought...If you want your piston to accelerate at the same speed as the BB, wouldn't the spring play a large role? Someone should find a way to calculate the speed of the piston...
     
  17. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    ^That would be fun for Airsoft Forensics. And a company back 10 years ago kind of did that in Canada...BBBastards.

    The piston and bb thing does not work because it uses Air pressure to transfer energy between the two objects under I believe the Bernoulli Principle of large volume to small volume.