KWA CQR FPS Lowering

Discussion in 'What Gun Should I Get?' started by CQB, Aug 4, 2012.

  1. CQB

    CQB New Member

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    If I had this gun would I have to get a spring with the power of 350 FPS? The reason for it is because the CQR's use the same gearboxes as the big boy ones but the cylinder is different. The different cylinder lets out more air I think because it lowers the FPS from the standard KWA spring which shoots at ~400 FPS. I need a FPS lower than 330 but higher than 290. (At 290 people can't feel it sometimes).
     
  2. thatoneguy

    thatoneguy New Member

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    Oh trust me, people can feel BBs at 290 FPS. You just need a different sized spring.
     

  3. Bulldawg26

    Bulldawg26 Active Member

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    The CQR cylinder is ported closer to the cylinder head. As a result, the piston doesn't start compressing the air until later in its cycle - thus the lower FPS. You can switch out the cylinder for a standard one from KWA's website and should get @ 400 fps out of it. (presuming you have a good o-ring seal). Otherwise, the CQR has the same 2GX gearbox as the SR10, KM4A1 and KM4 RIS.


    EDIT: By the way, you should get 350 fps out of a stock CQR.
     
  4. CQB

    CQB New Member

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    How should I get it to 330 FPS then?
     
  5. Bulldawg26

    Bulldawg26 Active Member

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    You'll probably have to drop down to a 100 spring. I don't think KWA has a cylinder that is ported more forward than the one in the CQR. Is 330 fps your field's limit? You can also call KWA's customer service line. That can probably give you some other ideas.
     
  6. CQB

    CQB New Member

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    Yea it's VERY strict at 330 with .2
     
  7. wookie

    wookie New Member

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    Your cylinder porting explanation was false. Fps is a result of air being pushed fast. So the faster the air is being pushed the more fps. That is the point of matching. Cylinder volume to barrel length. Maximixing acceleration. Cylinder volume is the ammount of air contained in the cylinder. You need a certain amount of air to get a bb out Of the barrel. So, ports in the barrel increase fps as long as it has enough volume to push the bbs.

    Also op a 100 spring will cut it close depending on how your compression is. For example I had 386+- 2 fps on an m100. You could drop to an m90 but premature engagement becomes an issue. I would look into short stroking on an m100 if it's an issue. The significantly worse option is making your. Compression worse.
    What battery are you using?
    And is the gun stock?
     
  8. Bulldawg26

    Bulldawg26 Active Member

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    Actually, I think you are missing the point. I agree that cylinder volume should match barrel length, but that is not the end of the story. FPS is based, in part,on the velocity of the air leaving the nozzle and propelling the bb down the barrel. That velocity is achieved by compressing the air in the cylinder through the nozzle in what is often called the Venturi Effect. Since cylinder volume is defined as Pi times cylinder length times the square of the cylinder radius and since there is essentially no compression of the cylinder air volume until the piston head pushes past the front edge of the cylinder's ports, the further back the ports are from the cylinder head, the more air is contained in the cylinder when the piston begins to compress it. As such, the piston is compressing a larger volume of air with ports located toward the rear of the cylinder than toward the front. Because this larger volume of air (from a rear ported cylinder) must pass through the nozzle in the same amount of time that the smaller volume of air (from the cylinder with more forward porting), it must speed up to exit the cylinder via the nozzle before the piston head reaches the cylinder head. This increase in air velocity results in higher psi against the bb. Since the air is "looking" for the path of least resistance, it accelerates the bb out of the barrel in what we measure as FPS.

    In this case, we know that that the volume of air in the CQR cylinder with ports a little more than halfway back (3/4 hole type) from the nozzle is sufficient to get a .20 bb up to about 350 fps as it leaves the inner barrel. Since the CQR effective cylinder length is shorter (3/4 hole type) than the effective length of a KM4A1 cylinder (4/5 hole type) and since we know that the 4/5 hole type cylinder in the KM4A1 gets .20 BBs out of the barrel of that gun at @ 400 fps, I estimate that switching the CQR cylinder with a standard KWA 4/5 hole type cylinder (like that found in the KM4A1 or KM4 RIS) will result something close to that velocity coming out of the CQR (with possibly some FPS loss due to the shorter inner barrel length in the CQR).

    The point of all this is that I was trying to answer CQB's question without getting too technical about the explanation. Changing the cylinder type would be an inexpensive method of achieving that goal of increasing FPS in the CQR if desired.


    CQB: I believe the CQR comes with a m110 spring. I would keep the stock cylinder but drop the spring down to a m100. That should get you down to below 330 fps.
     
    Last edited: Aug 19, 2012
  9. wookie

    wookie New Member

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    @bulldog I'm not even sure what you are trying I say. Your summary was in agreement with how I corrected you. Ported cylinder that matches barrel length = more fps than if it was a type 0. He wants to decrease fps. So, a full cylinder is an option. The full cylinder would lower fps because the air compresses from the nozzle is slower but in greater quantity.

    Also the ported cylinder isn't the reason the cqr wouldn't shoot as hard. There is always spring and compression differences..... But no that's too rational.

    This is a better explanation.
    [urlwww.airsoftcanada.com/showthread.php?t=18038[/url]

    @op just look at my last post.
     
    Last edited: Aug 20, 2012
  10. alex

    alex New Member

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    first, chrono your AEG with .20g. you might get lucky and get a leaky one at 320 fps.
     
  11. Bulldawg26

    Bulldawg26 Active Member

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    What I was getting at was that if you replace the stock KWA CQR cylinder with the stock KWA KM4A1 cylinder, the fps will likely increase from @350 fps to close to 400 fps. Presuming there are no other changes to the 2GX gearbox, hop-up and inner barrel, that is factually correct and also verified by KWA techs. It is ls also proven out by basic physics principles. If you would check my prior posts, you would also notice that I intentionally simplified the initial explanation for "conversational" purposes. I also suggested that CQB switch to a M100 spring to drop the fps to something under 330 fps.

    I read the link you referred to in your post. It is interesting reading but it isn't applicable here. I never suggested that CQB use a Type 0 un-ported cylinder. There is no "suck back" issue with a ported cylinder in the CQR. To avoid a potential cylinder volume issue, going to lower rated spring (i.e. M100) is a safer alternative to going with a Type 0 cylinder - especially when you are dealing with a 273 mm barrel in the CQR Mod 2.

    Obviously, there are going to be variations in spring "fling-back" and possible air leaks that could affect compression. Since anyone in airsoft will acknowledge that fact, I'm not going to bother responding to your "too rational" comment. Seriously?