What evidence supports the claim that a dual recoil spring reduces recoil?

This is a discussion on What evidence supports the claim that a dual recoil spring reduces recoil? within the Defensive Carry Guns forums, part of the Defensive Carry Discussions category; Originally Posted by Eaglebeak According to the literature I received, the manufacturer explained that intertwined dual springs were not only inconsistent in compression tension because ...

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Thread: What evidence supports the claim that a dual recoil spring reduces recoil?

  1. #46
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    Quote Originally Posted by Eaglebeak View Post
    According to the literature I received, the manufacturer explained that intertwined dual springs were not only inconsistent in compression tension because they could shift position with coils of one interfering with coil action of the other, but also the shifting of position would cause inconsistent drag force as they compressed along the guide rod and or could buckle/bulge enough to drag on the barrel as well. However, they went on to recommend replacement of the single slide spring more often than the recommended replacement of the dual springs because the single spring with larger diameter wire would tend to lose its tension/compression dymanics faster than two springs of smaller wire diameter. Since the Mustang has only a 2.75" barrel and very short slide throw (being a .380), I'm guessing that maintaining proper slide spring tension is critical to its reliable operation.

    So (at least with the Mustang), it seems like a heavier gauge single spring gives smoother and more consistent operation, but doesn't retain its original compression dynamics for as many compressions as two smaller diameter springs?
    Coil springs are conceptually simple, but there a number of design elements to be considered in making them work for any given application. There are a lot of misconceptions about coil springs.

    - You can design a spring to be compressed to its solid height without losing any of its spring rate, but the tradeoff may be an unacceptably large coil (not wire) diameter. Most coil springs in guns (recoil + mag springs) are not designed to be compressed to solid height.

    - All coil springs "relax" after a number of initial load cycles. This absolutely changes the free length of the spring, and is of little concern. Thus a recoil spring that's 6.0 inches long brand new but 5.75 inches long after 50 rounds (fictitious numbers for illustration) is behaving normally. Actually, when testing new springs for spring rate we cycle them a number of times ("conditioning") and measure the free length until it stabilizes before we measure spring rate.

    - on longer springs like the 1911 recoil spring, moderate "buckling" - not staying perfectly straight - while under compression has no significant effect on the spring force during the stroke.

    - once again, leaving a spring compressed to its designed working length (usually that's something other then the spring's solid height) causes no deterioration in its spring rate. Cycling the spring from compressed (to its design dimension) to relaxed will cause the spring rate to decrease over time. Just how many cycles to what level of reduced spring rate depends on the specific spring design factors and can be predicted with reasonable certainty. (Which means, follow the gun manufacturers' recommended replacement intervals!) Hence it's not the least bit surprising that a cocked-and-locked 1911 with a fully-loaded magazine sitting unused in a drawer for 50 years will still fire and function well... not a thing has happened to 'wear out' those springs in all those years.

    - stuffing springs into small spaces such as for the subcompact pistols like the Mustang or Officers Model entails compromises, typically spring life is chosen as the acceptable parameter to give up.

    - dual, concentric springs (a parallel spring arrangement) is one solution to getting "more spring" into a small space. With such a design, both springs could indeed be stressed less on each cycle than a single spring of comparable spring rate, and thus should have a greater replacement interval. The likelihood of concentric coils actually clashing with each other should be minimized by good design.
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  3. #47
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    Guys, if I may, a bit of course correction. A Harrt's recoil damper, that's never been scientifically evaluated or even tested informally in a way that produces actual numbers, is NOT a dual recoil spring. If a Harrts does reduce recoil by a humanly discernible amount, it only shows there are effective ways, probably more effective than dual recoil springs, to reduce recoil with a single spring.

    I just feel like we're drifting into the dangerous association that if something like a Haarts can reduce recoil, that some how proves a dual spring reduces recoil better than a single spring. But the Harrts is a single spring system. It would be interesting to replace a Glock plastic guide rod with a SS and a Harrts and see if we could tell which was which in blind tests.

    Smitty,
    I agree except for one point. Even top quality springs can loose strength if left compressed for extended periods of time. There are actually two known mechanisms at work. One is creep and the other is relaxation. Both are discussed here:

    Excerpted from: Relaxation and creep - Mubea Disc Springs

    Over time, all springs undergo a loss of elasticity. Depending on the type of load imposed on the spring, this loss of elasticity manifests itself as relaxation or creep.

    Relaxation is the decrease in force, ΔF, seen over time if a spring is compressed to a constant length Creep. One speaks of creep when the spring to which a constant force has been applied in time further decreases in length by an amount ΔI so that its overall height lo is reduced.

    The relaxation or creep of the spring under working conditions is decisively influenced by the following factors:

    Amount of load stress, which for practical purposes is expressed by ōI
    Residual stress condition result from the presetting process in production
    Working temperature
    Material strength, especially also at high temperatures (heat strength)
    Duration of load application
    This is also supported in field observations. One Glock armorer reported that when he does mag spring tests as prescribed by Glock as a part of maintenance for his LE department, he finds springs start failing the test between two and three years. While LE guns are shot some, i.e. very low mag spring cycles, the primary cause of fatigue is compression over time.

    Mecgar, Wilson Combat, Wolff Gunsprings, and some others all recommend unloading mags for storage and cycling mags.

    Mag springs in uber high capacity mags, like 18 round flush fit Mecgar mags, et al, for 92Fs, PX4s, P226s, etc. are more susceptible because the spring has to be driven to the 'knee' of the plasticity curve.

    Note this doesn't say a spring fails, it says it loses strength.

    Anyway, I'll get back on subject now.
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    Whew! For someone who's not an engineer, nor slept in a Holiday Inn Express, this thread is a brain-ful!! Still, I waded through all four pages...
    My take has been that multiple recoil springs were originally for compact and sub-compact guns, to soak up recoil energy over a much shorter distance than what's available with full-size guns. What comes to mind are the early "Officer"-size .45 autos, where the barrel and slide were at least 2" shorter than standard GMs. There were many comments about the difficulty of racking the slides against those recoil springs.

    For "full--size" guns, DRS' remind me of FLGRs, FSS' and light rails, and skeleton triggers; gadgets whose main purpose is wealth transfer.

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    OK, here are some pics as promised:
    I hope the size isn't too annoying, I left them big for the sake of seeing more or better details:



    This needs some explanation. The out spring appears to be fastened to the inner steel carrier at the right as shown in the picture.

    The inner spring looks to be a single spring but the end extending to the right appears to have a closer pitch than the rest of the spring.

    Both springs compress together from the start, i.e. there is no 'picking up' of the second spring like I first assumed.

    A close-up:



    A view from the end:



    and how it behaves as it compresses - is that the strangest spring thingy you've ever seen or what!!



    Notice that it appears that the inner spring has nothing to push against on the left end (as seen in the pic)! In the condition show in the pic, I can actually move the steel carrier back and forth as seen here:

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  6. #50
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    Quote Originally Posted by shep854 View Post
    Whew! For someone who's not an engineer, nor slept in a Holiday Inn Express, this thread is a brain-ful!! Still, I waded through all four pages...
    My take has been that multiple recoil springs were originally for compact and sub-compact guns, to soak up recoil energy over a much shorter distance than what's available with full-size guns. What comes to mind are the early "Officer"-size .45 autos, where the barrel and slide were at least 2" shorter than standard GMs. There were many comments about the difficulty of racking the slides against those recoil springs.
    LOL - sometimes 'mythbusting' by the nature of the beast gets very technical. Although I'm not sure we've busted anything other than my thumb trying to operate the recoil spring with one hand to make pics and a vid.

    Let me make a couple of comments about the Officer size .45s. First, you correctly identified the problem - there's not much room to put a suitable single spring. In order to get the spring rate needed, larger diameter wire would be needed. But larger diameter wire comes at a cost: loss of spring travel distance. I.e. the spring coils make contact with each other and prevents the slide from realizing a full travel cycle.

    If there is room to put two concentric springs, and I think gasmitty mentioned this too, the wire diameter can be smaller and the dual springs can relieve the travel limit due to spring collapse. But this is not to reduce recoil; this is to get the required spring rate in a short place.

    The reason the spring has to be stronger on smaller guns in a given caliber, e.g. the Officer vs full size, is a loss of mass in the slide. Two things control the slide travel and velocity, the mass of the slide and the force against the slide from the recoil spring. If you reduce mass, i.e. a shorter slide/barrel, you have to go up in spring strength to compensate.

    Quote Originally Posted by shep854 View Post
    ...For "full--size" guns, DRS' remind me of FLGRs, FSS' and light rails, and skeleton triggers; gadgets whose main purpose is wealth transfer.
    ROFL!!! Shhhh! You don't have to tell everything!

    Well there may be some truth to that, but there are people that find some of these things advantageous and wouldn't buy a gun without them.
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    "...there are people that find some of these things advantageous and wouldn't buy a gun without them."--Tangle
    True, but just sayin...

  8. #52
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    Quote Originally Posted by shep854 View Post
    "...there are people that find some of these things advantageous and wouldn't buy a gun without them."--Tangle
    True, but just sayin...
    I hear ya - I'm with ya.
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    Quote Originally Posted by gasmitty View Post
    OK, so what we need is to set the gun up with an LVDT or a velocity transducer on the slide (relative to the frame), maybe an accelerometer measuring muzzle acceleration in the vertical direction, and another accel on the rear of the frame (where one would grip the gun), and mount it all in a Ransom rest. Shoot the gun numerous times with standard and aftermarket spring configurations and maybe with a few different loads. Record the data at a high enough rate, maybe 10 k samples/sec... then we could see for sure what the differences are.

    That's the kind of test I get involved with in my biz... dynamic events on aerospace hardware.
    That's definitely on the right track..x-y accelerometers on the frame, to me, tell the whole story as far as perceived recoil, but instrumenting the slide will tell you what you're actually doing with your spring gizmo treatments. Since the 'whole system' is the weapon-shooter, and since the bulk of the story is told in the first couple of milliseconds, I'd like to see the data with the weapon being fired by a person, as well. I don't believe it would add much if any noise to the system, and it would permit full, real-world degree-of-freedom (including rotation about the bore axis). Possibly the most important degree-of-freedom is direct rearward motion of the entire system (along the bore axis) during the first millisecond or two.

    I think it would ultimately come down to: are you reducing jerk (rate of acceleration) anywhere in the cycle, at the frame.
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    I think the real question that should be asked is does it make the gun more reliable? I honestly think that there would be many folks on both sides of the fence on this.
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    Quote Originally Posted by Bongo Boy View Post
    That's definitely on the right track..x-y accelerometers on the frame, to me, tell the whole story as far as perceived recoil, but instrumenting the slide will tell you what you're actually doing with your spring gizmo treatments. Since the 'whole system' is the weapon-shooter, and since the bulk of the story is told in the first couple of milliseconds, I'd like to see the data with the weapon being fired by a person, as well. I don't believe it would add much if any noise to the system, and it would permit full, real-world degree-of-freedom (including rotation about the bore axis). Possibly the most important degree-of-freedom is direct rearward motion of the entire system (along the bore axis) during the first millisecond or two.

    I think it would ultimately come down to: are you reducing jerk (rate of acceleration) anywhere in the cycle, at the frame.
    Accelerometers on the slide would give the same information, plus slide motion characteristics. The slide would be more challenging to mount the accelerometers. One could contemplate mounting accelerometers to an interface that clamps securely on the rail of the slide. Of course that introduces frame flex.

    You have any particular accelerometers in mind? I can do the interface and data collection with either a microcontroller or computer. Just wondering if you had anything in mind for accelerometers and/or how/where to mount them.
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    Quote Originally Posted by C hawk Glock View Post
    I think the real question that should be asked is does it make the gun more reliable? I honestly think that there would be many folks on both sides of the fence on this.
    True, but I would think reliability data could come from just shooting. In the specific case of the Gen 4, both G22s and G17s, I think the answer is yes, it did improve reliability. In fact, what led to the development of the latest recoil spring, at least as I understand it, was LE agencies having reliability issues with a WML attached.
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    I think "felt recoil" is something that occurs WAY before the slide even begins to move. The actual energy [recoil] created by the velocity of the subject slide [mass] moving rearward will decelerate as larger (heavier) spring assemblies are incorporated.

    Slow doesn't equate to Less. Fast doesn't equate to More.
    What we've got here is failure to communicate.

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    @Tangle, thank you *so* much for the pix and the video. Now I can see what you are taling about.

    As to the moveable inner spring assembly in the Gen 4 spring, your comment, "It's just strange" is highly apropos. To put it mildly.

    Glock seems to have grasped the virtues of simplicity in design and manufacturing. That they are making such a complex (and weird) triple spring assembly with an inner carrier suggest to me that they were near their wits' end when trying to solve a problem with some springs, subject to some very stringent boundary conditions (of which cost was not the primary constraint).

    I have to go think more about this.

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    Quote Originally Posted by los View Post
    I think "felt recoil" is something that occurs WAY before the slide even begins to move. The actual energy [recoil] created by the velocity of the subject slide [mass] moving rearward will decelerate as larger (heavier) spring assemblies are incorporated.
    Partly. The recoil impulse begins as the bullet accellerates down the bore, and before the barrel has unlocked. The bullet accelerates forward and the entire gun accelerates backward. Meanwhile, the top of the tun tries to move backward but encounters resistance from the shooter's hand on the grip. The grip is below the line of applied force of the bullet accelerating down the bore, so the barrel begins to rotate upward (which is why iron sights are not parallel to the bore). The front of the grip begins to push against the fingers, which means that part of the recoil sensation is actually the front of the grip pushing against the shooter's fingers, which in turn means that how tightly and how strongly the shooter grips the gun influences the perception of recoil (both rearwards and forwards).

    Then the slide and barrel assembly unlock and the slide begins to accelerate backward after the bullet has left the bore (for a semi-auto). The slide travels backward encountering one or more different springs (all at the same time or perhaps serially) and eventually comes to the end of its travel and stops harshly. This deceleration of the slide is part of the perceived recoil, and the stopping of the slide is another part of the perceived recoil.

    Then, the polymer frame of the pistol (a Glock in our example) flexes, and further lengthens the recoil forces to the shooter's hand, lowering the peak impulse and lengthening the recoil force curve. I'm sure I have seen videos on YouTube of the frame of a Glock pistol flexing during the firing cycle.

    Then we have the issue of frame shape and width. My Glock 30SF gives faster split times for me shooting 230 grain hardball than my narrower all-metal HK P7M8 does. It is harder for me to get the gas-piston-damped, heavier P7M8 back on target that it is for me to get my G30SF back on target and to get the next rapid-fire aimed shot onto the target. Similarly, I can shoot faster on-target splits with my G30SF than I can with a G19 (Gen 3).

    Finally we have the issues of how thick the shooter's hand is (how much muscle tissue is between the back of the gun's frame and the bones in the shooter's hand) and how much the shooter's elbow is bent. I feel more perceived recoil when I shoot with a straight (not locked) elbow then I do when I shoot with a bent elbow.

  16. #60
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    Possibly GLOCK decided to copy the HK recoil spring set-up because HK has been using a SPRINCO type spring set-up effectively for many years.
    I'm not that familiar with H&K handguns & only just aware of the fact that the double spring system is not new or innovative.



    And my apologies for tossing your thread off-topic w/ the Harrt's. It was unintentional on my part.

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