Magazine Springs

[JSmith]

Like most of us, I keep a firearm(s) loaded just in case something bad happens. Do semi-auto-shotguns & semi-auto mags experience spring failure in the magazines or tubes if they're kept loaded for long periods of time? Should the designated "emergency gun" be swapped out periodically?

 

[rcmodel]

Not that I've noticed.

I have kept 1911, AR-15, Ruger Mini-14, and a host of others fully loaded for 40+ years with no effect on the springs.

I have bought WWI 1911 mags, and 1936 Colt Woodsman mags at estate sales with 1917 .45 ammo and pre-war copper case .22 RF made back then still in them.
They still work fine.

I have read reports of shotgun mag springs weakening over time.
But I have never experianced it as I don't keep shotguns loaded indefinately around the house.

I do down-load Glock mags by a round or two in storage, as they are over-compressed when fully loaded by design.

Springs wear out from cycling, not from static compression.

But If it worries you?
Down-load them by a round or two.

And I gayRonTee Ya any quality mag springs will last way longer then you will.
If you don't wear them out cycling them!

rc

 

[JSmith]

Thanks, rc! That's good to know.

 

[LUCKYDAWG13]

springs wear out from use not compression

 

[Drail]

Springs wear out from use AND over compression AND cheap poorly tempered steel. Not all springs are made from quality steel. But you'll be the first to know when the last round won't feed cuz the spring died. I have seen several tubular magazine springs in shotguns fail from long term full compression (cruiser guns). But a bigger problem in shotguns is shell deformation from long term compression. Some shells will swell and bind in the tube. Not good at 3 AM in the dark. You should download by one for long term loading and/or buy high quality aftermarket springs (Wolff or ISMI) and change them once a year. Cheap insurance. The factory springs will be from the lowest bidder. No thanks.

 

[chiltech500]

If you search on this forum you will find someone who did testing on mag springs and he did find deterioration over time from just storage.

 

[Drail]

Yup. Saying that "springs only wear from cycling and not from compression" is a GROSS oversimplification. There's a little more to it than just that. Most firearm manufacturers buy springs in gross bulk quantities and tend to compensate by overspringing the gun in an attempt to get long life and a lower failure/return rate. If your springs came from the lowest bidder all bets are off as far as how they will hold up. Buy quality springs, don't overload them for long periods and expect to replace them when they begin to show weakness. They're not expensive and they are absolutely necessary for the gun work reliably.

 

[barnbwt]

"if they're kept loaded for long periods of time?"
Noop.

"Saying that "springs only wear from cycling and not from compression" is a GROSS oversimplification."
Saying that springs only suffer from cycle fatigue unless plastically/permanently deformed is exactly what is the case. Even a spring loaded up to its yield point (absolute worst for fatigue endurance) once and held there will suffer no degradation. A spring deformed past its yield point (the popular 'breaking in of springs' we hear about) can suffer micro/macro cracks in the process and suffer reduced life; but will only further degrade if loaded cyclically.

"don't overload them for long periods"
Damage is done by the overload within a fraction of a second; the grain boundaries have slipped, the spring has plastically deformed, and no further movement occurs. Better advice is to not overload your mags (ever) unless springs can be easily sourced (seems to only be a real issue in little pocket guns with short magazines that really squeeze in as much as they can)

Stress corrosion might be a thing in certain steels (I only know for a fact it's a very real issue in aluminum alloys) but proper maintenance should prevent that being an issue in guns.

TCB

 

[fletcher]

Magazine spring force will weaken over time as a function of stress and temperature - this is known as stress relaxation, and is a documented phenomenon. Some mag springs can handle being loaded for extended periods, some can't. It depends on design, materials, etc. This can and does happen when loaded below the yield strength of the material.

However, they will fail (i.e. break) only by repeated cycling (fatigue).

That being said, my mags stay loaded. My Makarov and 1911's primary magazines have been loaded near continuously for 8 years, and to this day they don't have problems cycling. Note both are single stack magazines.

 

[Longhorn 76]

When was the last time you had a valve spring fail in your car?

 

[fletcher]

Past threads discussing this same question with more information:
http://www.thehighroad.org/showthread.php?t=679572
http://www.thehighroad.org/showthread.php?t=721240

Just because a valve spring has not failed does not mean that it did not lose some strength during installation and/or service. An intact and properly functioning valve spring means that the designers accounted for relaxation and stresses to ensure proper operation. Its operating conditions are also different from magazine springs, so the comparison is apples and oranges.

See http://www.shotpeener.com/library/pdf/1976001.pdf:

An automotive valve spring is a good example of a spring operating under constant deflection. The spring is manufactured to a certain free length, but when installed it is compressed to fit into the available space and create a specific preload. In operation, the spring cycles continually over a constant stroke length or deflection. In time, depending on material, stress, and temperature, the spring may relax and reduce the applied load. Usually, though, valve springs are designed to minimize relaxation and thus, deliver loads within a specified range.

Also, from the Navy's Handbook of Reliability Prediction Procedures for Mechanical Equipment:

Static springs can be used in constant deflection or constant load applications. A constant deflection spring is cycled through a specified deflection range, the loads on the spring causing some set or relaxation which in turn lowers the applied stress. The spring may relax with time and reduce the applied load.

 

[rcmodel]

Mr. John Browning & other firearms designers understood all that when they were designing magazine fed guns in the early 1900's.

Without an engineering degree of any kind.

Unfortunately, today, many very well educated gun designers have lost that intuitive knowledge, and error on the side of mag capacity vs compressed spring yield points over a lifetime of being loaded.

rc

 

[Drail]

Absolutely on point RC. People always bring up the story of Grandpa's single stack 1911 that was left loaded for 60 years and fed and fired the whole magazine perfectly. They apparently knew how to make a quality spring in the Old Days. Today - almost know one cares or spends the money for quality springs. (and unknowingly designs them to be overloaded and believes that "springs only wear from cycling") If you're running a double stack magazine don't push it too hard. It's probably already being pushed to or past the limit. A single stack magazine is in an entirely different category.

 

[4thPointOfContact]

How does the metal in the spring know if it's being used in a double or single stack magazine?

Is 4 inches of spring compression in a double stack magazine fundamentally different than 4 inches of spring compression in a single stack mag?

 

[fletcher]

A double stack configuration places more stress on the mag spring. More force is required to place rounds in a feeding position as compared to the simple linear push against the feed lips for single stacks.

 

[Drail]

Double stack magazine designs are generally designed to get the maximum number of rounds in the magazine. Browning's original single stack 1911 magazine was designed for absolute reliability and service life. He allowed plenty of room for the spring and follower. The spring was compressed to a load level far below its elastic limit. The spring lasted a very long time. Of course later generations just had to "improve" upon it and use all of that "wasted space". I'll take absolute reliability and long service life every time over "extra" rounds and a grip that is too wide to get my hands around (compared to a single stack. Today however it seems that everyone is obsessed over how many rounds they can cram into their magazine. And I think that poor marksmanship has a lot to do with that. You can either hit with the first shot and every shot or you can spray and pray. You really can't make up for missing a fast critical shot with more rounds. But that would seem to be the "New Technique". Flame me boys and girls.

 

[barnbwt]

"Just because a valve spring has not failed does not mean that it did not lose some strength during installation and/or service. An intact and properly functioning valve spring means that the designers accounted for relaxation and stresses to ensure proper operation. Its operating conditions are also different from magazine springs, so the comparison is apples and oranges."
These are valve springs; were these observations of stationary engines held at temperatures a magazine would see in storage, or of an engine running several thousand rpm at several hundred degrees?

The thermal relaxation phenomenon occurs at the lowest reaches of the tempering curve, right? So wouldn't that be several hundred degrees, minimum? Dunno about ya'll, my mags don't get that hot in the gun or storage. I wouldn't want to fire ammo that heated, that's for darn sure.

I always thought double-stacks required a stronger spring due to A) the extra inherent friction of a double stack design on the side walls, and B) shoving up the mass of additional rounds fast enough to be snagged by the returning slide. FWIW, PPSH mags are ancient and are still good, as are the drum mag clock springs (Suomi's are even better, since both were made slightly nicer than the Russian copy-cats). Compared to feed lip distortion due to fatigue or out-and-out damage (mag drops, anyone?) seems to be a far more significant factor effecting good mags. It is quite true that you need to start with a good spring; I can imagine softer springs having issues with relaxation/etc. since they operate way closer to their yield point, and are therefore less consistent (yield point is an observed average; each time you approach it those slip planes let go at slightly different times near the yield point; crummy steel will have a wider variance)

TCB

 

[Longhorn 76]

Maybe it lost something in the translation concerning the valve springs. The point being that a properly designed spring, operating within the yield values is the steel, works forever. If you have crappy springs, in a mag that pushes the steel past it's yield, you will have problems.

 

[fletcher]

Maybe it lost something in the translation concerning the valve springs. The point being that a properly designed spring, operating within the yield values is the steel, works forever. If you have crappy springs, in a mag that pushes the steel past it's yield, you will have problems.

Exceeding yield will cause problems, I agree with that. However, staying below yield is not a guarantee of performance. I'll explain this further below.

The thermal relaxation phenomenon occurs at the lowest reaches of the tempering curve, right? So wouldn't that be several hundred degrees, minimum?

Yes and no. There are different metallurgical mechanisms at play - the scenario you reference is one of them, and will certainly result in relaxation. However, it is not the only way relaxation occurs. Other mechanisms are either thermally activated or have a thermal component, but they are also active at room temperature.

It’s Saturday morning and I have some time to explain this further, so be warned – wall of text ahead.



If the temperature is near or over the tempering temperature for steel, further tempering of martensite will occur. Martensite tempers as carbon diffuses and subsequent phase transformations occur. Phase transformations will relieve some of the stresses.

When closer to room temperature, other mechanisms cause relaxation. A major one is transformation of metastable phases due to the addition of strain energy. Metastable phases are present in most any steel. Examples are martensite, which is a key phase used to strengthen steels, and retained austenite, a high temperature phase that is stabilized enough by alloying to stick around at room temperature.

These phases are stable enough for practical purposes, but are not at the lowest energy state and will transform if given an opportunity. Strain energy introduced by compressing a spring is enough to push the phase over the edge so to speak, and cause some fraction to convert. This is addressed in About the Structural Mechanism of Stress Relaxation in Metastable Alloys, by Grachev. Here are some excerpts from his paper which may help explain:

At the initial moment of loading the entire strain is elastic, i.e., ε0 = εel . With growth in the hold time a part of the elastic strain transforms to plastic strain.

For alloys with a high portion of metastable phases, like steel, there is a time-dependent component to elastic loading. It’s not as sudden or pronounced as with polymers, but some of the initial strain (ε0), which is elastic (εel) and fully reversible, will turn into plastic strain (εpl). This means that a loaded spring which has had any amount of its elastic strain convert to plastic will not fully restore to its original condition when unloaded. Therefore, it will have taken a slight set and lost some of its force.


Here’s one of Grachev’s graphs showing relaxation over time for a certain steel alloy at various elevated temperatures. The y axis shows relaxation as σr/σ0, or the relaxed stress (after a period of time) over the initial stress. The x axis is time in minutes.

It’s pretty clear that the amount of stress lost in the spring increases with increasing temperature. It is important to note that the loss is not sudden - this is not a case of yield strength being exceeded! There is a gradual loss of strength to an approximately stable level. This behavior alloys the educated or experienced designer to account for relaxation. Transformation or decomposition of martensite is the likely cause for relaxation in this case. A very important note is that this behavior can vary drastically from alloy to alloy, and even between different heat treated conditions of the same alloy – this is only one example (hardened U8A steel).


Here’s a particularly interesting example from the same paper. This one is a 70S3KhMVA steel which has some degree of retained austenite. As the temperature decreases from 20C (68F) to -196C (-321F), more relaxation occurs – completely backwards from the previous example. How does this happen?

As noted earlier, austenite is normally a high temperature phase in steel – in a plain carbon steel, temperatures of 1333F or higher are required to make it appear. The addition of certain alloying elements can stabilize austenite enough to be retained at room temperature. Further cooling forces the transformation of this metastable phase to proceed. It’s not necessary to hit -321F to transform – this is an extreme case used in the paper. In this case, a fully loaded magazine exposed to a North Dakota winter could actually lose more strength than one seeing an Arizona summer. Retained austenite is very common in hardened steels, and is usually present to some small extent. Most of the time it’s not an issue, but bad heat treatment, improper material selection, etc. can result in more retained austenite than desired.


The American Society for Testing of Materials (ASTM) released a collection of Selected Technical Papers (STP) specifically concerning stress relaxation testing. In ASTM STP676 is a paper titled Room-Temperature Stress Relaxation of High-Strength Strip and Wire Spring Steels – Procedures and Data, which contains the above graph for room temperature stress relaxation of a strip spring steel (not coiled wire). The difference in behavior between alloys can be seen pretty clearly.



I’ve thrown a lot of information out here, and hopefully it’s enough to help show what happens in a loaded spring. There are a lot of variables in relaxation of springs - design, alloy, heat treatment, service temperature - but it has been known for decades that relaxation does happen. In a properly engineered spring, the user would never know the spring lost force because the design accounts for this phenomenon. There are companies and designers out there that, for whatever reasons, are unaware of things like this – as such, there will be good and less-than-good magazine springs floating around.

Just because some springs work flawlessly when loaded for an extended period does not mean every spring will. The fact that so many people in the gun community debate this really goes to show that by and large, the magazine spring designers are doing a very good job. However, cases of weakened springs pop up with some regularity.