Brownells on Buffer (and other) Springs

BY Herschel Smith
1 year, 2 months ago

Okay we’ve covered this before.

So there is yet another post about magazine springs and whether they should be replaced, and if so, when.  This is in the same theme I wrote about several years ago when there was another little flurry of articles and posts about this.  I’m going to cover this ground one time for everyone.

Metal creep is caused from slippage of crystalline structures along boundary planes, whether FCC, BCC, or whatever.  One reader writes that “springs don’t wear out from compression.”  This is along the same lines as most of the [mistaken and incorrect] articles I linked the last time I addressed this issue that claimed that stainless steel doesn’t creep below the yield limit.

Do you know any piano tuners?  I do.  Yea, they have to go back a few days later and retune because of metal creep.  But most piano wires are carbon steel under high stress.  What about stainless steel?

Do not make the claim that stainless steel (like SS304) doesn’t suffer creep below the yield limit and at low temperatures.  Yes … it … does  (“In all tests at applied stress/yield strength ratios above 0.73 some plastic deformation was recorded”).

No offense, but don’t try to be an engineer if you’re not one. If you make the claim that SS304 (I presume the material of most magazine springs) doesn’t suffer from metal creep, you’d be wrong, and then you’d also be answering the question the wrong way.

The right way to look at the question is one of whether the creep is significant.  It usually isn’t, and it is less significant than for carbon steel.  It’s also not significant for applied stress/yield strength ratios lower than what the authors tested.  Where your specific magazine spring falls in this data set is best determined by the designer, not me (I don’t have drawings or any other design information).

Stop saying that it’s only the compression / decompression cycle that puts wear on springs.  Stop it.  Just stop.  That’s not true.

It … is … not … true.

It’s true enough that the compression / decompression cycle is fatigue wear, but it’s also true that this means slippage of the crystalline structures just like metal creep.

Again, the question is whether this creep is important under the specific design circumstances or not, whether the specifications are challenged or not.  It’s not about whether creep will occur.  It does, and it will, even if undetectable by you.

I’m not saying here that it’s a bad idea to leave your buffer spring compressed.  I’m not saying that it’s a bad idea to leave your magazines full of rounds.  Don’t misunderstand what I’m asserting.  I’m not even asserting that Brownells was wrong in their conclusions, even if they didn’t do all of the necessary analysis to properly arrive at their conclusions.

I am asserting that the justification for whether you do or don’t leave springs compressed has nothing whatsoever to do with whether the spring undergoes a compression / decompression cycle while it’s in the configuration it’s in.

It has to do with a materials and structural engineering analysis that most people don’t do (and probably don’t need to do), and which Brownells didn’t do for the video above.

This may sound like a nit, but not to an engineer.


Comments

  1. On March 15, 2023 at 12:42 am, Rick said:

    I think the never ending debate over magazine springs is because of variety in materials and munfacturers. IOW, some do, some dont.

    Obviously, all due for that is the nature of all materials. Yet some springs don’t show wear as much as others.

    F’rinstance, recently I found one of the mags for an AK had a noticeably weak spring. I had kept the mag fully loaded.

    Yet not one of ten rotary mags for a Ruger 10/22 has shown any noticeably wear of the spring. Four mags stay fully loaded, six stay empty until immediate use. Indeed, the 10/22 mags are years longer in service than the AK mags.

    So, if I were to decide the debate based only on one type of mag for one caliber, I might decide yea, or nay, dependant on which type mag, caliber, mfg, age.

    I stay out of such discussions (this being my first comment ever on this ongoing debate). I observe but decide for myself to regularly service my equipement per .mil or mfg advisories.

  2. On March 15, 2023 at 6:03 am, Latigo Morgan said:

    I’d say the answer to the question is, “It depends.”

    I’d also say, “Probably not in your lifetime.”

  3. On March 15, 2023 at 7:34 am, ragman said:

    Check out the Sprinco website. I have installed their buffer springs and extractor springs in my sporting equipment. Also they provide excellent videos on how to tune your gas, bcg and buffer spring for the best performance. I have a couple of Adventure Line mags from the Vietnam era with the original springs and they work great.

  4. On March 15, 2023 at 9:46 am, Thomas Madere said:

    Think about the valve springs in your vehicles engine and how many times it cycles yet failures are extremely rare even in racing engines. this whole magazine spring business is silly.

  5. On March 15, 2023 at 10:16 am, Herschel Smith said:

    Those are fabricated differently and have a different spring coefficient. I also suspect they operate no where near a ratio of 0.73 — by design.

  6. On March 15, 2023 at 4:54 pm, JB said:

    I am surprised that no accredited group or individual has done empirical testing on say a STANAG 5.56 mm magazine, or at minimum computer simulations on appropriate modeling and design software to put this age old question to rest. It would be a good research project for a Phd student. Perhaps DOD has something buried in their archives.

  7. On March 16, 2023 at 3:10 pm, Chris said:

    If compressed springs were a problem, my Browning Superposed would be a mess. Instead it’s still operating as designed after 70 years. When the shotgun is cocked, the mainsprings and ejector springs are compressed. When fired, the ejector springs are still compressed. If it is opened, the ejectors trigger releasing their springs, but doing so also cocks the mainsprings again. One set or the other (or both), springs are always compressed. Clearly not a design issue!

  8. On March 16, 2023 at 3:41 pm, Herschel Smith said:

    You utterly missed the point. I didn’t say spring compression is a problem in most, if not, situations we will find ourselves in for firearms.

    What I said was that it’s wrong to assert that the reason for this is that SS304 doesn’t sustain creep at all.

    That’s not true. Depending upon spring ratio, stress and yield strength, it’s possible for SOME plastic deformation to occur.

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You are currently reading "Brownells on Buffer (and other) Springs", entry #34327 on The Captain's Journal.

This article is filed under the category(s) AR-15s,Firearms,Guns and was published March 14th, 2023 by Herschel Smith.

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