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my "long term" observations of loaded magazine springs in my Mossberg 590

Discussion in 'Shotguns' started by Sheepdog1968, Oct 2, 2012.

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  1. Zoogster

    Zoogster Member

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    My experience tells me that it is often the last round left loaded that causes the spring the most wear from just sitting.

    A spring is meant to work within a certain range of compression. In many guns the last shell compresses the spring so much that if you let it sit that way long term is has a much greater impact than all the other shells prior.

    Think about it. Measure the shell you are putting in (some can be slightly longer than officially depending on crimp), add up the length of them all and subtract that from your magazine tube. How much space is left over for the spring. Do you really think a spring that long should be that compressed?
    Sometimes the spring gets so compressed it folds over itself or gets mashed sideways. So it is not even being stored compressed straight up and down as designed, but is slightly deformed with a load in a direction it was not designed for.
    This issue is greater wth some barrel lengths and extension tubes that match the barrel length because some just barely let that last shell fit and so compress the spring more. While others have an extra inch or two giving a little more slack. After you load the last shell in, see how much you can push it down the tube with your finger. Assuming its not already smashed out of shape, that will tell you how much space it has to sit without being fully compressed or compressed beyond fully compressed. In some guns there is nothing. Compressing a spring 100% wears it a lot more than compressing it 90%

    That is why I avoid the threads that say it is only the spring being worked that leads to wear, and not sitting loaded. Yes that is true if the spring is only being compressed within the ideal range. But often that last round takes them beyond that. I especially see this more in magazines designed for locations that limit capacity by law. Some of the 10 round magazines for California are designed so there is absolutely no possible way an 11th round could be smashed in there, even if the base plate was bowed and someone with mental issues insisted on crushing one in there. They accomplish this by making that 10th round barely fit in there with the spring so smashed it is deformed and crushed against the bottom of the magazine. The last round is so tight it has no slack at all and cant even be pushed down a little.
    That is not the compression level a spring is intended to be at. Crushed at the bottom.
     
    Last edited: Oct 5, 2012
  2. JohnKSa

    JohnKSa Member

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    From what I have been able to determine, you're definitely on the right track.
     
  3. fletcher

    fletcher Member

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    You rang? :p

    This is one of those fun topics that never seems to get resolved. I've always been from the "a properly designed spring should not lose any noticeable amount of strength under static load" camp, and have made a couple posts in the past here with this view. Yesterday, I gave this thread a read and decided to do a bit of research to find what the underlying mechanism is behind loss of strength under static conditions, or stress relaxation (as with the paper Sam Cade referenced), in hopes of enlightening myself and coming to a definite conclusion.


    Springs may lose strength after being loaded to a static condition (let's assume it's only one time, so fatigue isn't in the picture) in three ways:

    1. The spring was overloaded (yielded) at some point when getting to the static condition.

    2. The temperature is high enough that creep occurs. Creep is a thermally activated, time-dependent process which becomes significant at approximately 1/2 the melting point (in degrees Kelvin) and above. Depending on composition, steel melts at ~1650-1800 °K, so 1/2 melting point would be ~1025-1160°F.

    3. Stress relaxation.

    The mechanism behind stress relaxation is a bit less intuitive than those behind #1 and 2, but is pretty neat from a metallurgical perspective. Short answer - energy in the system due to loading, residual stress, surface energy, etc. can attain a point where metastable phases in the alloy convert to other phases, thereby relieving some of the stress. That may be a bit of a mouthful, but I'll try my best to explain what this means if people are interested (it would certainly result in a wall of text).
     
  4. Uniquedot

    Uniquedot Member

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    I'm interested and would assume others that have posted in the thread would be too.
     
  5. Fred Fuller

    Fred Fuller Moderator Emeritus

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    If you're willing to post it, I'm sure willing to read it...
     
  6. Sheepdog1968

    Sheepdog1968 Member

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    Agreed.
     
  7. fletcher

    fletcher Member

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    Warning - incoming wall of text as promised. I’m usually discussing this sort of thing with other engineers, so if I’m using too much jargon or if something doesn’t seem clear feel free to ask and I’ll clarify.

    For this explanation, let’s assume we have a steel spring loaded to capacity. I’ll also need to touch on some definitions/basics:

    Phase – Metals are composed of one or more sets of structures internally, which are known as phases. The formal definition is “A homogeneous portion of a system that has uniform physical and chemical characteristics.”

    Equilibrium – State where the phase(s) will remain stable indefinitely. This will be a point where the free energy is at a minimum.

    Energy – Energy in the system can come from many places, such as temperature, surface area (including internal surface area between crystals), elastic deformation, and amount of mechanical work (plastic deformation) put into the material. The first three are the most important here.

    Phase Diagram – This isn’t particularly important for the explanation in itself, but I think it will be a good visual aid. For a certain combination of elements, this will show which phases are the equilibrium states. The iron-carbon (Fe-C) phase diagram (below) is the most important one for steels. The X-axis will be in either weight or atomic percent, and the Y-axis is temperature. In short, it shows the stable/preferred phase(s) at a combination of concentration and temperature. These diagrams are put together by calculations and/or experiments at various temperatures and compositions.

    [​IMG]

    From the above diagram, we can see that the stable phases in a carbon or low alloy steel at room temperature are ferrite (α-iron), cementite (Fe3C, a carbide), and pearlite. Pearlite is a lamellar combination of the first two. The picture below shows a pearlite structure - the light bands are ferrite, the dark bands are cementite.

    [​IMG]

    Even though the above three phases are stable, often other phases present at room temperature under certain conditions. While the stable phases are certainly useful, they don’t really fit the bill when trying to get something of very high strength or hardness. This role is filled by a phase known as martensite, and it is used extensively in steel products to attain upper-end strength. Martensite is obtained most commonly in the following ways:

    1. Rapid quenching from elevated temperature where the room temperature stable phases (ferrite, pearlite, cementite) aren’t present. This works because the stable phases rely on diffusion to form. Because diffusion is temperature dependent, cooling the alloy down rapidly “freezes” the process, and does not allow the stable phase(s) to form when cooled. Martensite is formed with a “diffusionless” transformation; that is, it does not require diffusion to form. Instead, the atoms do an extremely short-distance shuffle and pop into place so to speak. For example, with an extremely rapid quench, the resulting structure would be pure martensite. Quenches can be tailored to obtain various percentages of this phase.

    2. Mechanical deformation/working. Some steels, notably a few 300-series stainless steels, can transform to martensite when deformed or otherwise worked. This type of martensite has the same structure as that in #1, but is known as “strain-induced martensite”.

    This is where the magic starts to happen. Looking at the stable phase diagram, martensite is nowhere to be found, so why does it exist? By subjecting the alloy to certain conditions, a “metastable” phase has been created and locked in at room temperature. This happens when a phase is created in a localized low-energy state, but isn’t at the lowest energy.

    In the image below, three example states are shown on a plot of energy (Y-axis) vs. position (X-axis). Martensite would reside at position #1, where it is pretty stable, and the stable phase(s) would be at position #3. Given the opportunity (enough energy to bump the system up to #2), the structure will try and go for the lowest-energy state. In the case of stress relaxation, that opportunity comes in the form of added elastic energy from our loaded spring.

    [​IMG]

    When the extra energy is added to the system by compressing the spring, enough energy may become available to transform a bit of that metastable phase. In doing so, it has converted the elastic energy into a permanent change in the alloy. This will show up as some reduction in the spring force. This reaction would continue until some finite amount of the phase has transformed, at which point the elastic energy would be lower than the required energy to bump it over and stabilize. Stress relaxation curves will confirm this with a rapid drop followed by little to no subsequent loss over an extended period.

    Since greater compression means more energy in the spring, Zoogster’s comment that it is often the last round which caused the set seems pretty reasonable. Maybe the spring is just fine until that last round or two gives just enough oomph to start the transformations.

    One of the papers I looked at, Structural Mechanism of Stress Relaxation in Metastable Alloys by S.V. Grachev, showed that thermal energy also contributes to this transformation. Increases even to 200°F, well below the creep temperature, combine with the elastic spring energy to cause noticeably more stress relaxation. The reverse is also true, where the same load will produce less relaxation at cryogenic temperatures.

    Hope this is decipherable enough to provide some insight to the issue.
     
    Last edited: Oct 6, 2012
  8. Uniquedot

    Uniquedot Member

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    Yes it was very informative. I've done some reading on metallurgy in the past and was somewhat familiar with many of the changes you discussed. When things interest me I'll read up on the subject til i lose interest and the knowledge is generally lost with the interest. Thanks for taking the time to post this.
     
  9. Fred Fuller

    Fred Fuller Moderator Emeritus

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    Thanks for that presentation.

    It seems leaving room for a slug in the magazine when a defensive shotgun is loaded does more good than just saving time if 'select slug' is called for right off the bat.
     
  10. JohnKSa

    JohnKSa Member

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    I suspect that this is the case in most situations where a spring obviously weakens from being left compressed. Either because the designer decided that a spring is an easily replaceable (essentially disposable) part, or because the quality of the spring wasn't quite what it should be or because other design parameters were more stressing (in terms of what the designer was trying to achieve) than long spring life.

    Frankly, these days, I don't hear about it happening nearly as often as it did back when high-capacity, double-stack pistol mags were first becoming common and every maker was doing their absolute best (worst?) to stuff an extra round or two into the mag in an attempt to remain competitive in the market.
     
  11. Gary A

    Gary A Member

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    Whew! You guys are smarter than me. Let me ask this:

    I use a standard 870 police model for home defense with a 4 round magazine. Since I only have 4 in the magazine I am reluctant to download by one round. However, the magazine will hold four three inch shells so it seems to me that loading it with four 2 3/4 inch shells (as I do) saves that final "inch" of compression and should prevent the extra strong police model spring from being over-compressed. I also avoid loading it with bargain loads like Sellier & Bellot which are crimped differently and have a longer OAL. I stick with Big 3 loads. Am I wrong? I have seen no degradation in the springs in the past several years.
     
  12. PT92

    PT92 Member

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    I was almost certain of your findings but read your post verbatim--Wonderfully useful information as this is a topic of perpetuity in the forums and the net at large.

    -Cheers
     
  13. Sheepdog1968

    Sheepdog1968 Member

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    For me, the most important aspect was the actual data I collected on my shotgun. If yours seems to be fine and you check it every now and then, I wouldn't worry about it.
     
  14. Sheepdog1968

    Sheepdog1968 Member

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    I'm glad you found it useful. It took quite a few years to collect the info. My biggest driver was I just wanted to make sure the shotgun would work as intended if I ever needed it.
     
  15. SSN Vet

    SSN Vet Member

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    Flether,

    You are more cruel than you can possibly know...

    By posting that wicked phase diagram, you have triggered a "post tramatic stress" relapse for me, resulting in flashbacks to my undergrad days :neener:

    For some reason, all the MMM (Metalurgy, Mechanics, Materials) Department faculty at State were from India, and I couldn't understand a word my Metalurgy 101 prof said.

    Now I'm waking up in the middle of the night in a cold sweat shouting out things like "chloride stress corrosion of Austenetic stainless steel" :eek:
     
    Last edited: Nov 1, 2012
  16. SSN Vet

    SSN Vet Member

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    Though this sounds really hot... much hotter temps can be seen in desert environments.

    I designed several of the foam inserts for hard shell cases (Pelican & Storm)used to stowe PackBots (EOD robots similar to the Talon used in the movie The Hurt Locker). Most of the foam assembly is done with hot melt adhesive, but we received feedback that the lid foam was falling off in cases used in Iraq.

    It turns out that the cases were often strapped onto Humvees in the direct sunlight, and the hot melt adhesive was softening up and the lid foam assemblies were dropping off under their own weight.

    For the record, the hot melt adhesive we use doesn't flow untill heated up >300 deg. F.

    We solved the problem by switching to a spray contact adhesive and changing the case color from black to a less energy absorbing tan color.

    also of interest...

    My co-worker is a USMC reservist who tells me that they download M4 mags to 28 rounds, as that is more reliable than loading them to the max capacity of 30.

    Apparently 300 deg + max. compressed mag. springs = unreliable feeding from mags
     
    Last edited: Nov 1, 2012
  17. AI&P Tactical

    AI&P Tactical Member

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    If it do or if it don't, think about this. A Magazine spring for an 870 in either 4 shot or 6 is only $3.20. If your defense shotgun is your go to gun and you can't spend $3.20 once a year or even once every two years to ensure the best feed possible then you must feel you have no serious need for a dependable defense weapon.

    I am not a rocket sceintist and came up with the above answer. Sorry there are not charts, graphs and formulas involved in my humble response.
     
  18. Snowdog

    Snowdog Member

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    I plan on keeping my 590 loaded for HD and haven't any concerns. I left my Maverick 88 loaded for such use from the mid-90s to just recently and it never failed to function.
     
  19. PT92

    PT92 Member

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    Agreed-I have always subscribed to the theory that the only way to weaken a magazine spring is to flex it past its normal range (elastic limit). If this is happening, somebody is trying to overload a magazine or has "adjusted" it by bending the spring. Both of these could cause feed failures.
     
  20. Sheepdog1968

    Sheepdog1968 Member

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    Nothing wrong with that. The whole reason I ended up doing what I did was to make sure the primary home defense weapon would be reliable. As this went on over the years I thought it might be good info to pass along so I eventually did.

    I am a practicing scientist. Both experiments and theory are important. At the end of the day, I prefer experiments. Unrelated to this but similar in nature is my beloved 30-30 lever action with a 16.75" barrel. I could spend all day calculating POA/POI all the way out to 400 yards (I don't shoot animals beyond 200 but will shoot steel out to 400). I prefer to just collect the data and have a really good set in 25 yard increments out to 100 yards with between 5 & 10 shot groups. I will likely be gathering data in 25 or 50 yard increments all the way out to 500 yards just so I know.

    At some point I will get around to chrono data at muzzle so I can eventually plot theoretical vs. actual data just for the heck of it.

    On similar threads I see discussion on twist rates and bullet weights. At one point, I took my mini-14 out and at 50 yards shot from low 40 grain to mid 70 grain ammo to see if I could observe differences. Given the accuracy of the weapon plus me I couldn't (3 MOA give or take one MOA).

    Most of these measurements/experiments have made for fun days at the range as it's something different.
     
  21. forehire

    forehire Member

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    Springs

    "Wolf, wolf, Wolf"
     
  22. Drail

    Drail Member

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    You need to ask yourself which is more important to you - having that extra round stuffed in the mag compressing the spring fully - or having a magazine that will feed every round every time. And Wolff springs are higher quality than what most manufacturers install in their guns at the factory. All springs are NOT the same. Yours may have a high quality properly tempered spring or you may have a spring from the lowest bidder. I used to stuff my shotgun mags full and leave them that way for years and never worry about the spring. Experience has taught me that was not such a good idea.
     
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