Is keeping a large capasity mag full result in failure to feed?

[SSN Vet]

FWIW...

My coworker is in the USMCR and is qualified as a range coach. We've been to the range with ARs several times and he tells me that they are taught to download by two to 28 total. But I believe this is to ensure the mags seat fully when slapped into place. Topping off a 30 rounder requires more force to seat the mag and thus, higher potential to fail to fully seat the mag in a rushed, high stress environment.

Poor spring design can have the spring stressed beyond it's elastic limit when fully loaded. If this happens, the spring will take a permanent set after the first couple loadings and may no longer apply enough force over it's full range of motion to reliably feed.

A lot of times, people bring up creep, but creep usually only happens when a metal has been exposed to high temps, or constant stress applied over a long period of time that is close to the metals yield stress. For mag springs, neither of these would be likely.

Also, there was a very interesting write up by a guy who was a metallurgist why was discussing phase change that can happen within the metals crystalline structure when a stress is applied over a long period of time. This can change the mechanical properties of the metal.

A well designed mag. with geometry right for the spring, and good spring metal (Chrome Silicone or High Tension Carbon Steal) should not have any of these issues and should only be susceptible to fatigue after being cycled thousands of times.

 

[Warp]

FWIW...

My coworker is in the USMCR and is qualified as a range coach. We've been to the range with ARs several times and he tells me that they are taught to download by two to 28 total. But I believe this is to ensure the mags seat fully when slapped into place. Topping off a 30 rounder requires more force to seat the mag and thus, higher potential to fail to fully seat the mag in a rushed, high stress environment.

Yes, downloading by two helps ensure it seats fully, especially when inserting on a closed bolt

But most would recommend a push/pull insertion, not a slap.

 

[GLOOB]

If you are using Russian lacquer-coated ammo, then the answer could be yes. The pressure between rounds can cause them to fuse together just enough to cause feed malfunctions.

 

[strykerfire]

Drail, I have seen magazine springs fail, too. But they all have one thing in common: Junk spring material and cramming ten pounds of crap in a five pound bag. Cheap "knock-off" mags will fail whether they are high cap or not. Mags that try to cram in extra rounds without altering spring design or length will fail.

Cramming in those extra rounds means over compressing. Taking anything outside its intended parameters results in failure sometime. Junk spring material is self explanatory.

I've had chipMc power mags fail so good ones will to. Lets say it holds 12 i put 9 in it why? Because if i cant deal with a self defense situation with 9 im not using very good judicial marksmamship and that aint cool man... Not cool at all.

 

[Arizona_Mike]

Springs should not wear our from years of being compressed but I've seen it a couple times including a Mossberg 590 spring that went totally soft. Should it occur, it's just a spring and cheap and easy to replace. I keep mags with metal lips and metal-reinforced lips loaded. They only polymer lip mags I keep loaded have stress-relieving "dust" covers that keep the force off the lips.

Mike

 

[Warp]

Springs should not wear our from years of being compressed but I've seen it a couple times including a Mossberg 590 spring that went totally soft. Should it occur, it's just a spring and cheap and easy to replace. I keep mags with metal lips and metal-reinforced lips loaded. They only polymer lip mags I keep loaded have stress-relieving "dust" covers that keep the force off the lips.

Mike

I'm pretty sure Magpul will tell you there is nothing wrong with leaving their PMAGs loaded pretty much indefinitely.

 

[Sam Cade]

I'm pretty sure Magpul will tell you there is nothing wrong with leaving their PMAGs loaded pretty much indefinitely.

I've had one loaded since 2008 without distortion.

 

[fletcher]

This discussion happens frequently enough that I'm considering running a quantitative test to evaluate different springs.

It's in the brainstorm stage, but I'm thinking of setting up an inexpensive load cell with data acquisition to generate a relaxation curve for a sampling of springs over the course of a month or two (or however long it takes to show). For example, 5 different spring manufacturers for a specific kind of magazine. Thoughts? Anyone have knowledge of such things to provide advice?

 

[Drail]

Ask any LEO armorer about pump shotguns that sit in racks for years with stuffed magazines (and only fired once per year) about how well the springs held up. One of the reasons Brownells sells them in bulk packs.

 

[Warp]

Ask any LEO armorer about pump shotguns that sit in racks for years with stuffed magazines (and only fired once per year) about how well the springs held up. One of the reasons Brownells sells them in bulk packs.

Mine's fine...been keeping it with a stuffed magazine for...8 years so far.

 

[Arizona_Mike]

I'm pretty sure Magpul will tell you there is nothing wrong with leaving their PMAGs loaded pretty much indefinitely.

The PMag covers push the top round down slightly releaving all stress on the lips.

Mike

 

[Warp]

The PMag covers push the top round down slightly releaving all stress on the lips.

Mike

I am aware and I stand by my statement that Magpul will probably tell you there is no problem keeping their PMAGs stored loaded pretty much indefinitely.

 

[Zach S]

I had an early one fail... Just like the colt/metalform 9mm SMG mags are known to. Spit a good bit of the ammo out of the top...

I haven't used the covers since I tried stuffing one in a magwell... I only load 28 rounds like the rest of my mags, most of which are milspec aluminum. Well, more like a pile of milspecs and a handful of PMags.

 

[RustyShackelford]

What you can do & what you should do.....

I agree with most of the forum remarks, there are few shooters or gun owners that are going to use modern firearms or magazines to the point that they wear out.
Now a cop or service member could be issued a wore-out firearm or weapon with feeding-cycle issues but that's not the same as buying a gun then cleaning/service for it's lifetime.

Extreme temps, rough use, bad weather etc can damage or wear out almost any item too. Not just firearm magazines.

Many years ago, in the late 1990s, I read how several LAPD officers had to re-qual with pump 12ga shotguns so old & poorly maintained they couldn't even go thru a police session without a misfire or jam.
At the time, the LAPD issued Ithaca 12ga model 37s & 870 shotguns.
In 2014, I think they now use 590/500s Beneli Super 90s & a few other well made brands.

Downloading a few rounds or shells isn't a bad idea but it's not critical to most shooters either.

 

[HOME DEPOT GEORGE]

I had a problem with Para P14 mags that I left loaded to capacity for about a year and they wouldn't lock the slide back until I took them apart and stretched the springs.

 

[1KPerDay]

This discussion happens frequently enough that I'm considering running a quantitative test to evaluate different springs.

It's in the brainstorm stage, but I'm thinking of setting up an inexpensive load cell with data acquisition to generate a relaxation curve for a sampling of springs over the course of a month or two (or however long it takes to show). For example, 5 different spring manufacturers for a specific kind of magazine.

I'd be very interested in seeing that. The common belief is that there is NO effect on springs from keeping them fully compressed, and I've parroted that statement myself.

HOWEVER, the same people will advise new Glock owners that have trouble loading the last round in their mags to "keep it fully loaded for a week and it'll get easier to load the last round." So it's clear that there is SOME impact on springs from storing them fully compressed.

I've also had a Mossberg 590 mag spring "go bad" after not too many cycles, and I always keep it fully loaded (8 rounds in the tube). I wonder if the quality of the spring may have more to do with its resistance to failure in this regard than we commonly assume.

 

[Sam Cade]

HOWEVER, the same people will advise new Glock owners that have trouble loading the last round in their mags to "keep it fully loaded for a week and it'll get easier to load the last round."

Or they could just depress the follower a few times with a pen.


What appears to be going on is that the springs haven't had their set done by the manufacturer.

When a custom spring is supplied longer than specified to compensate for length loss when fully compressed in assembly by customer, this is referred to as “Allow for Set”. This is usually recommended for large quantity orders to reduce cost. When a compression spring is compressed and released, it is supposed to return to its original height and, on further compressions, the load at any given point should remain constant at least within the load limits specified. When a spring is made and then compressed the first time, if the stress in the wire is high enough at the point the spring is compressed to, the spring will not return to its original height (i.e., it will get shorter). This is referred to as "taking a set", or "setting". Once the spring is compressed the first time and takes this set, the spring will generally not take any significant additional set on subsequent compressions.

http://springipedia.com/compression-stress-spring.asp

 

[rcmodel]

Initial spring 'set' is normal on a new spring when it is first fully compressed.

But once the initial set takes place, very little to no more will occur from staying compressed.

Cycling the spring will eventually wear it out.

Here is an interesting new spring test from Brownell's.
http://www.brownells.com/.aspx/lid=...t-Between-Different-Types-of-Spring-Materials

rc

 

[fletcher]

I'd be very interested in seeing that. The common belief is that there is NO effect on springs from keeping them fully compressed, and I've parroted that statement myself.

I'll tentatively plan on doing this experiment. I have no experience using load cells, but this will be added to the list. Seems like it would be well worth the relatively small investment to put some real data into this debate.

 

[Doc7]

Thank you. That confirms what I did learn in the Army. An M16 mag can actually hold 21 in an 20 round mag but its tight and we were told not to do that.

A spring should not get weak from compression.... But OVER compression may damage it...

 

[svtruth]

Think

about your car or truck that sits on its springs for years

 

[fletcher]

about your car or truck that sits on its springs for years

Automotive suspension springs also take some sort of set and can relax to some extent over time. "Spring sag" is a catch-all term describing the symptom in that industry - mechanisms causing sag include stress relaxation. There are numerous papers on the subject (handful cited below), and plenty of people who report leaf springs sagging in older vehicles. It may not be apparent on the vehicle(s) you drive, but it does happen, and a lot of R&D has gone into minimizing the effect.

Kawakami, H., et al. Effect of chemical composition on sag resistance of suspension spring. No. 820128. SAE Technical Paper, 1982.

Murai, Teruyuki, Seizo Takamuku, and Nobuharu Takeno****a. High sag resistance spring wire for automotive suspension. No. 850059. SAE Technical Paper, 1985.

Borik, F., V. A. Bišs, and Y. E. Smith. Sag Resistance of Si-Mo and Si-Cr Spring Steels. No. 790409. SAE Technical Paper, 1979.

 

[Zach S]

Apples and oranges.

If you were to work out a ratio in respect to their free, installed, and compressed lengths, automotive springs aren't compressed near as much as magsprings are.

And they do wear. Take a look at any early 80s to mid 90s ford truck - they didn't sit three inches higher in the back when they were built. Later 4wds arent so bad, but the early two wheel drives are easy to spot Due to the front end sag.

 

[rcmodel]

I am of the opinion that automotive spring sag happens over time, and lots of driving.
(Cycling) ie: Shooting a lot of ammo through a mag.

I don't think it would happen at all if the car was left parked in your driveway an equal length of time.
(Static load) ie: Leaving a mag loaded over time.

rc

 

[fletcher]

Part of the problem with using sag as an example is that it describes a symptom. The symptom could have multiple causes - stress relaxation, wear (e.g. fatigue), overload, etc. There are research papers which document stress relaxation testing methods with reference to sag resistance, so it is known that relaxation under constant load/displacement is a concern.

The paper I cited above by Borik is an example - exactly the same mechanism as a mag spring being loaded:

The sag resistance was determined by room-temperature relaxation tests in which the specimens were stressed in tension for 150 hours under a given plastic strain.