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 Hopyard Agreed. I'm a bit uncertain about exactly what you are referring to as a DRS. Here's what I'm thinking....Situation 2) I ...

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  1. #31
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    Quote Originally Posted by Hopyard View Post
    Agreed.

    I'm a bit uncertain about exactly what you are referring to as a DRS. Here's what I'm thinking....Situation 2) I have another gun in which the springs are arranged entirely differently. What I think they have achieved is an approximate doubling of the spring length by the way the springs move counter to each other within one "container."

    This is where I think maybe your analysis is not quite 100%. "But a spring cannot provide additional movement." That depends on how the double spring is arranged.
    The motion I was referring to is the motion of the slide. I'm assuming the motion of the slide is limited by a solid lock between the slide and frame when the slide is in battery and a fixed stop between the slide in frame when the slide is fully rearward. Hence a spring cannot increase the distance the slide travels.

    So, since a G17 Gen 4 has a dual spring, and quite an interesting one, I took the spring out and checked the motion with the spring out. Then I re-installed the spring and rechecked the slide travel. It is exactly the same either way. The only thing that a longer spring could do is perhaps completely collapse, i.e. coil to coil, which would reduce the amount the slide could travel.

    Lets take two springs with the very same spring constant. One spring is 4 inches long and the other is 8 inches long. it will take exactly the same amount of force to compress either spring by the same amount. Of course until the shorter spring nears full collapse.

    ------------------------------------------------------------------------------------------------------------------------------

    A lot of this goes back to what Bongo Boy said in post #21 and #26. I agree completely with all that, in fact, that's what I've been saying in different words. I would add to Bongo Boy's remarks that we cannot overlook how the mass of a recoil reduction device affects recoil. I suspect replacing the plastic guide rod in a Glock with a solid SS would have more of an effect on actual recoil and perceived recoil than dual springs would.

    I've been playing with my G17 gen 4. I slowly pulled the slide from full forward to full rearward. I can feel no dual spring rate, not discontinuous spring rate - it behaves exactly like a single, linear compression spring. But, tomorrow, I'm going to get a 5/16" dowel and actually measure the spring rate at two points. What I've 'felt' tells me that this dual spring is going to behave just like a single spring. In fact, a common 'fix' for the improper dual spring in a gen 4 G17 is to buy a bushing and replace the dual spring with the gen 3 G17 single spring.
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  3. #32
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    Quote Originally Posted by QKShooter View Post
    The Harrt's actually does "eat up" some energy that is expended in the fracturing of the liquid Mercury metal & that happens right at the instant of cartridge detonation so it works on an entirely different principle than an added secondary recoil spring.

    I know that it does allow the muzzle to come back down on target in a bit more of a hurry.
    I believe that it does have some real advantage though it is certainly not any sort of 40% or 50% reduction of anything.
    I would best guess 15~20% max but, with no function related disadvantages AKA there is nothing "mechanical" to ever break.
    The Mercury just stays forever sealed up inside the Stainless recoil spring guide.
    I've had it installed in my SIG firearm for many years now.

    "The Harrt’s Recoil Reducer was simple and well made, showing no outward flaws in workmanship. It relies on a reciprocating mass made up of mercury and ball bearings enclosed in the rod to dampen recoil.
    Essentially, the mercury and ball bearings provide inertia that lower the rearward recoil of the pistol.
    The Harrt’s device weighs about 2 ounces, and the heavy liquid mass encased in the rod tries to remain stationary as the gun begins its recoil cycle and adds forward mass after its inertia is overcome.
    It has no means of being rebuilt, but examining units that have been used by competitive shooters for two years show,
    I’ve seen little wear or peening where it is hit by the slide. To install it, you simply remove the original guide, spring, and recoil spring cap, replace the guide with the Recoil Reducer rod, replace the slide on the frame, and reinstall the recoil spring and proprietary cap supplied by Harrt’s.
    The assembly is then anchored as normal with the barrel bushing. It was easy and straightforward to install the Harrt’s product."

    Here is one cut open so...imagine it also filled with Mecury metal.
    I'm not sure I really by the mercury part. What happens when the balls wind up at one end and can't move in the direction they need to?

    Also, back in the day, I called Harrts and asked them how they determined what the percent of recoil reduction was. I was told by feel.

    Mercury is one of the heavier metals. Steel objects will float in it like a cork. So again here we see a stainless steel tube filled with a very heavy metal. Which would all by itself reduce muzzle climb and it's at the exact location it needs to be to be most effective. So I'd have to assume if there was a 20% increase in mass due to the mercury.....
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  4. #33
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    But, I think all this goes to show that out of all this discussion, nobody, not even Harrt, has actually ever measured recoil objectively.

    As several have noted, the slightest change becomes a marketing gold mine. They don't have to say it's so little that a human couldn't possibly sense it.

    We need blind tests and perhaps a recoil measuring machine. Until I see real data, I'm not buying that dual recoil systems can reduce recoil any more than a single spring, except due to the increased mass of the spring assembly.

    Speaking of that, I just measured the weight of a gen 3 recoil spring assembly and the weight of a gen 4 recoil spring assembly. The gen 3 weighed 10 grams; the gen 4 weighed 20 grams. So there's your recoil reduction right there! But it's not because of the dual spring, it's because the mass the mass of the gen 3. BTW, that doesn't in any way mean recoil is halved.

    But, I bet if we could measure the weight of a gen 3 SS guide rod, the weight would probably be more than the gen 4 dual spring assembly and we could claim the single spring gen 3 has less recoil than the gen 4 dual spring system. But I doubt a human could tell the difference.
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  5. #34
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    "But, I think all this goes to show that out of all this discussion, nobody, not even Harrt, has actually ever measured recoil objectively."

    So True So True.

    Then there are the Variable Chrome Silicon recoil springs which are single recoil springs that are differentially hardened & tempered.
    So the rearward slide travel (with a "variable" installed) starts out lighter & then gets progressively stiffer as the spring further or fully compresses.
    It would seem that single spring would do everything a twin spring system would accomplish w/ one less spring.

    Great thread Tangle.

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    Quote Originally Posted by QKShooter View Post
    Tangle you might think this article is interesting. Take it for what it's worth.

    June, 96 Recoil
    I am using a vintage (no longer being made) Harrt's installed in my P220 because I can tell that it will get me back on target a bit quicker during rapid fire.
    I have an old Haarts in my 1911. It really does help reduce muzzle flip.

    That aside, Tangle has the right of it in this thread. Spring constant K1 for the lighter longer spring, spring constant K2 for the second, shorter spring. K1 acts through the first part of the slide's movement, then the sum of K1 and K2 for the remainder of the slide's travel.

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    Quote Originally Posted by OldVet View Post
    Sheez, I'm so lost now. Who cares how it works as long as it does.
    Lots of us due to reliability concerns.

  8. #37
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    Quote Originally Posted by QKShooter View Post
    "But, I think all this goes to show that out of all this discussion, nobody, not even Harrt, has actually ever measured recoil objectively."

    So True So True.

    Then there are the Variable Chrome Silicon recoil springs which are single recoil springs that are differentially hardened & tempered.
    So the rearward slide travel starts out lighter & then gets progressively stiffer as the spring further or fully compresses.
    It would seem that single spring would do everything a twin spring system would accomplish w/ one less spring.

    Great thread Tangle.
    Thanks QKS!

    I have to admit I'm not seeing why Glock went to the dual spring system. The Gen 3 spring assembly costs about $5. The gen 4 dual spring assembly costs about $20, so it's not to cut costs, and it's a more complicated device so it wasn't to cut corners. I don't believe it was an attempt to reduce recoil at all. It may be as Glockman10mm said - to make it reliable with WMLs. I'm aware that was a problem with the G22 gen 4, but wasn't aware it was a problem with the G17 gen 4s.

    From my cursory look at the gen 4 dual spring assembly, it feels like it behaves exactly like a single rate spring, but it is quite a complex system. I'll try to get some pics of it up tomorrow. Very curious arrangement. It is by no means a simple concentric spring.

    The Glock Gen 4 dual spring assembly is like none I've ever seen. Both springs are engaged from the start and appear to remain engaged throughout the stroke.
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  9. #38
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    Quote Originally Posted by Tangle View Post
    But, I think all this goes to show that out of all this discussion, nobody, not even Harrt, has actually ever measured recoil objectively.

    As several have noted, the slightest change becomes a marketing gold mine. They don't have to say it's so little that a human couldn't possibly sense it.

    We need blind tests and perhaps a recoil measuring machine. Until I see real data, I'm not buying that dual recoil systems can reduce recoil any more than a single spring, except due to the increased mass of the spring assembly.

    Speaking of that, I just measured the weight of a gen 3 recoil spring assembly and the weight of a gen 4 recoil spring assembly. The gen 3 weighed 10 grams; the gen 4 weighed 20 grams. So there's your recoil reduction right there! But it's not because of the dual spring, it's because the mass the mass of the gen 3. BTW, that doesn't in any way mean recoil is halved.

    But, I bet if we could measure the weight of a gen 3 SS guide rod, the weight would probably be more than the gen 4 dual spring assembly and we could claim the single spring gen 3 has less recoil than the gen 4 dual spring system. But I doubt a human could tell the difference.
    Just thinking aloud though, that is only a 1/3 ounce difference in mass on something that weighs 22 ounces (G 17). Might as well drill a hole in the bottom of the receiver near the muzzle and attach a 1/2 ounce sinker -- Someone else do the math. Will that really translate to something one can actually feel as a difference?

    You are right, some sort of machine is necessary to get a real answer; or lots of testing by impartial participants giving subjective evaluations without the participants knowing what the mechanical set up is.
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  10. #39
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    Quote Originally Posted by marcclarke View Post
    ...Tangle has the right of it in this thread. Spring constant K1 for the lighter longer spring, spring constant K2 for the second, shorter spring. K1 acts through the first part of the slide's movement, then the sum of K1 and K2 for the remainder of the slide's travel.
    You are exactly right, but my original impression of the assembly was inaccurate. I've now discovered that the Gen 4 assembly is quite a bit more complicated than a simple dual spring system. I'll have to look at it some more and post some pics.

    Still by the action, i.e. feel, it feels quite linear and has no noticeable changes in the spring constant. It looks like it may b,e in effect, three springs arranged in a series-parallel configuration.
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    The principle of fracturing liquid Mercury metal as a transmitted shock/vibration dampener has been tested.
    Not specifically for the Harrt's though.
    For the Gamma Tenex Shock Watch.
    Which (same principle) AKA Mercury filled bubble in a watch worn tightly on the wrist. The best treatment against tennis elbow!
    But, is migratory vibration dampening related to recoil dampening/reduction.

    I have absolutely no idea. ~~~>

    Tenex® Elbow Shock Absorber absorbs the vibrations whenever your elbow is subjected to sudden impact such as golf, tennis, baseball, hammering, pounding or typing on a keyboard.

    Engineering Studies conducted at the Massachusetts Institute of Technology (MIT) and at HAKO Research Laboratories, concluded that the Tenex® Elbow Shock Absorber reduces migratory vibrations by 50 - 70 percent making Tenex® the most effective treatment against tennis elbow and carpal tunnel syndrome available today.

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    Quote Originally Posted by Tangle View Post
    Well, I asked for evidence. What we've all submitted is theories with no support behind it.

    RK,
    You've hit on the idea. I don't know that I can agree with your conclusions. But what you described is exactly what a DRS does. It's a lighter force over a certain distance followed by a heavier force over the remaining distance. I think the average force would be the same as a single recoil spring.

    And guys, we may be being 'sucked' in by manufacturers claims about DRS reducing recoil. If it is true that they do even by as little as 0.5% then manufacturers can claim reduced recoil. There's no way on earth a human could sense or feel that small of a difference.

    BTW, I'm not saying it doesn't, I'm asking what evidence do we have that it does and I think as a part of that, by how much?
    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.
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    Q: Anyone know the definition of an "Engineer"?

    A: An accountant with no personality.

    Good thread and lots of good information (what I understood)....but its time for a couple of Excedrin Migraine tabs.
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    Quote Originally Posted by Tangle View Post
    Eaglebeak, it doesn't work that way. The only property of a spring be it single or dual that can slow the slide down is the spring constant. To slow down the slide with a spring you'd have to increase the spring constant. But if you increase the spring constant and hence the force, the slide energy will be absorbed quicker and the slide will stop in a shorter distance. But then you can achieve that with either a dual or single spring. If you slow the slide down very much the slide won't travel far enough to fully extract the case or pick up the next round.
    I think you might have misunderstood my too lengthy response since I fully agree with your thoughts on spring dymanics, and I've seen many instances where people would try using heavier springs (or dual springs) to help take the sharpness out of recoil and only end up with a malfunctioning pistol because the heavier spring tension slowed the slide speed and/or didn't let it travel far enough to the rear to eject and feed properly.

    I would still like to see actual tests results of any device that actually reduces the total amount recoil force without changing the mass(weight) ratio between the pistol and the bullet being fired under the same propellant force. Once all the algorithms of mass/inertia ratios between two objects with a given amoung of confined force applied between them are figured, there will be a calculated amount of energy applied to the pistol as recoil force moving it in the opposite direction as the much lighter projectile is moving. While there are a number of "shock-absorbing" devices that broaden the curve of energy transfer (to your hand or shoulder), there is nothing to my knowledge that makes any of that energy somehow just disappear and go away. The shock-absorbing devices really do help with a "perception" of less recoil and do help control muzzle rise because they lengthen the time constant of recoil energy transfer into more of a firm "push" instead of a sharp "jolt", but the total energy applied remains the same.

    I also use the Harrt's Recoil Reducer in a couple of my pistols, and it's an excellent "shock-absorber" that (as mentioned) greatly lengthens the time constant of total recoil energy to give more of a firm push rather than a hard jolt. Additionally, the Harrt's RR actualy does reduce the recoil force by some degree, but not by any "magical" energy-sucking internal black hole. When figuring the additional weight of the device full of heavy mercury and shot balls, it increases the overall weight of the pistol which, in turn, increases the mass/inertia ratio between gun and bullet that actually does result in less "recoil" energy being applied to the heavier pistol. If there was some way of clamping a pistol in a recoil measuring device of some kind, I'd make book on the fact that it would measure a slightly higher recoil force with every shot because the pistol would weigh a little less with each round that was fired and ejected.

    I've sailed off course again from the original wonder about dual slide springs vs a single spring, and I am just as confused as anyone; but I tend to agree with others' thoughts that it's more of a performance or reliability issue than anything to do with recoil "smoothing" because it's already a given that increasing spring tension by too much will quickly cause malfunction problems with reduced slide speed and travel. I too have a Colt Mustang (old original Series '80) that came with dual slide springs of the same length that were intertwined with each other. A subsequent kit I bought to replace the plastic spring guide with a stainless steel guide came with only a single spring that had the same tension and progressive compression dymanics as the original two springs had. However, the information that came with the kit might help explain the question we're all pondering.

    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?

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    Quote Originally Posted by Tangle View Post
    You are exactly right, but my original impression of the assembly was inaccurate. I've now discovered that the Gen 4 assembly is quite a bit more complicated than a simple dual spring system. I'll have to look at it some more and post some pics.

    Still by the action, i.e. feel, it feels quite linear and has no noticeable changes in the spring constant. It looks like it may b,e in effect, three springs arranged in a series-parallel configuration.
    I only have a Gen 3 G30SF, so I don't have a Gen4 spring assembly to play with. I am listening intently.

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    I want a strain gauge on the back of the grip of the Glock in the Ransom Rest, please. I want to measure force on the web of the hand as the pistol fires and the slide comes back.

    Just so I have my mental image correct, the integral of the area under the force curve is the total recoil, and the peak force is the perceived recoil, right?

    A polymer buffer (such as I used to use in my 1911) would cushion the peak recoil when the slide hits the end of its rearward travel and decelerates to zero velocity. Such a buffer smears out the force curve (widens it) and lowers the peak of the force curve. Thus the perception of decreased recoil (less sharp recoil).

    A spring pack won't completely decelerate the slide to zero velocity, as there has to be some rearward inertia in reserve to overcome drag from mud and crud in the slide's rails. An optimum spring pack will weaken over time, so a new spring pack will have the slide impact against the frame at the lowest lifetime velocity. As the spring fatigues the slide's velocity will increase (slightly) and recoil will increase slightly over the lifetime of the spring.

    I don't think that lateral flex of the polymer guide rod has any role in recoil reduction, but I have not thought that one through yet.

    I'm just thinking out loud. Sanity checks welcomed.

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