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Thread: Action Spring Analysis

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    Action Spring Analysis

    I wanted to know the force for each common spring at the L1 length of an AR carbine, so I put a digital scale on my mill and adjusted it so that there would be 6.902 space between the scale and the head. I then inserted each spring between the scale and mill, inside a clear tube.

    I measured the wire diameter of each and the OD. I counted the number of coils. I input them all into spring design software, and it estimated the stress as a percent of the material's tensile strength. I then sorted each spring from least to most stress while at full recoil. The lower the stress as a percent of MTS, the less likely it will be to fatigue (take a set). If you see any mistakes, please let me know.





    Last edited by rsilvers; 12-09-11 at 08:43.

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    Thanks

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    Just to clarify, according to that data, there is no difference between the stress developed in 17-7 (Colt) springs and CS (Brownells) springs of the same geometry?

    I've got to get my hands on that software
    Last edited by Eric D.; 12-08-11 at 20:28.
    B.A.S. Mechanical Engineering Technology

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    Very interesting post.

    How much real-wold data exists on these springs?

    Reason I ask is that I've seen colt carbine action springs get noticeably weaker shooting a steady diet of M193 from a 6920 in as little as 3,000 rounds (A-B'd with a fresh spring and the 5-person group vote was unanimous that the new spring felt 'stronger').

    I know Gunz has had very good luck using the Springco Blue, which I use currently as well. I think he's at or past 10K rounds on hs Springco Blue in an SBR.

    I realize that the above are calculations and I'm not disputing them; I'm NOT an engineer. However, is there a source for real-world testing on this?

    I'm not one of the fanboy's who thinks that he can get 100K or even 50K compression cycles from his action spring before replacement...but the CS springs from Springco do seem to last longer than the 17-7 Colt springs I and my fellow LEO's have used before.

    I'm interested to hear what you have to say...and thanks for taking the time to compile all this data.
    Last edited by BufordTJustice; 12-08-11 at 21:32.

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    Quote Originally Posted by Eric D. View Post
    Just to clarify, according to that data, there is no difference between the stress developed in 17-7 (Colt) springs and CS (Brownells) springs of the same geometry?

    I've got to get my hands on that software
    That is pretty much what it is showing. It actually thinks CS and Music Wire are virtually identical, and 17-7 is a little better than either (if given the exact same inputs). I was not aware there was a case where 17-7 was better, but maybe it has to do with the Wahl stress correction calculation for this particular geometry. It sure seems like the original designers knew what they were doing.

    Here is a good book on springs:

    http://www.scribd.com/doc/29044778/S...esign-Handbook

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    Quote Originally Posted by BufordTJustice View Post
    I know Gunz has had very good luck using the Springco Blue, which I use currently as well. I think he's at or past 10K rounds on hs Springco Blue in an SBR.
    Let's assume that is true (and I would not accept it as true without the spring going on a scale setup like mine every 500 rounds and then a curve plotted), then one of two things may be happening:

    One - it has so much force that the recoil of the BCG is not able to compress it as much, and so it is not stressed as much. And if one liked that effect, they could just make a 17-7 spring with more force.

    Or two - maybe there is something to CS, such as being more shock resistant than 17-7. I did read that music wire and CS are both the top choices for shock resistance.

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    Quote Originally Posted by BufordTJustice View Post
    Reason I ask is that I've seen colt carbine action springs get noticeably weaker shooting a steady diet of M193 from a 6920 in as little as 3,000 rounds (A-B'd with a fresh spring and the 5-person group vote was unanimous that the new spring felt 'stronger').
    One would have to put it on a scale like I did when new, and then retire it when it reads 5.3 lbs - and then see how many lbs it dropped per 1000 rounds.

    I actually do this to decide when to throw away a spring. I just threw away a CS one which was at 5.3 lbs. I am not sure what it started at though, so I have no proof it dropped a lot.

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    Don't forget to measure the rifle spring in the A5 configuration.

    That is a real good one.
    Last edited by Clint; 12-08-11 at 22:55.
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    Out of curiosity how is the machine not just reading force applied (weight) instead of stress? what formula is the software using to compute the percentage? when taking the OD and wire diameter did you take multiple measurements over the length of the coil and then average them when compiling inputs for the computer? I'm not knocking at all what you did here, just a curios calibrator. In fact more of these types of post would make a Physical/Dimensional Tech (nerd) very happy.... As always thanks for your time....!
    You have enemies? Good. That means you've stood for something, sometime in your life.----Sir Winston Churchill

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    Quote Originally Posted by BufordTJustice View Post

    Reason I ask is that I've seen colt carbine action springs get noticeably weaker shooting a steady diet of M193 from a 6920 in as little as 3,000 rounds
    From
    http://www.spring-makers-resource.ne...ng-design.html
    Quote Originally Posted by Spring Makers Resource
    Advanced Spring Design: Stranded Wire Springs


    Long springs with many coils subjected to high rates of load applications, as in automatic weapons, encounter shock-wave motion or displacement of spring coils. The spring can be literally torn apart. Stranded wire springs are often the solution to such problems. This is because of the frictional resistance set up by the selective movement between strands.
    I believe this is the cause of early spring set.

    These shock waves would cause localized compression or stacking.


    What is the calculated spring life is compressed down to solid height?
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

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