...Given that springs can be designed to survive an extreme number of compression-decompression cycles, I assume they can be designed to survive to be stored for a long time under maximum intended compression. For a defensive firearm, any spring that cannot do this must be regarded as substandard. I believe the general sign of spring fatigue indicating a need for replacement is when a mag no longer feeds reliably.
Some of what you state above is correct, but there are exceptions. With some gun designs, the space available for the spring to do the work just isn't great enough, and the spring can be INTENTIONALLY over-stressed by the designer!
Back when Rohrbagh was still in business – he has since sold some of his designs to Remington and retired – the Rohrbagh R9 was the smallest 9mm you could buy. The recoil (a coil) spring originally had a recommended service life of 300 cycles. After selling a number of R9s, Rohrbagh recommended changing the recoil springs every 200-250 cycles. (Beyond that point the springs might still function, but their reliability was getting a little spotty.) The spring were very inexpensive, and they were, in effect, RENEWABLE RESOURCES. (I have an RM380, which is his R9 modified to run the .380 round. That recoil spring has a service life of 1000+ cycles.)
Rohrbagh's design was to be a true pocketable 9mm semi-auto, and to make a gun that would meet his SIZE and FUNCTION criteria, he had to use a pretty small recoil spring. For a spring that could be hand-cycled (when loading the weapon) and still have a long service life, that spring would have to be larger than the spring that could be made to fit in the space available with his design. A shorter-lived spring was the alternative, and because the springs were cheap, and the guns weren't meant to be shot a lot, that was his solution -- one that gave him function and size, if not long spring life.
Not all mag springs are compressed close to their elastic limits when fully compressed.
Tell us, if you will, WHY and HOW cycling damages the metal? Where and when does the spring material begin to get damaged? And tell us why cycling less deeply, like never pressing a 15-round magazine beyond the 10-round limit seems to have much less effect on spring life? And why would Wolff Springs recommend downloading mags a round or two for long-term storage if ONLY CYCLING damages a spring. (If they want to sell more springs, they ought to keep quiet on the subject!!)
As I've noted before, I've had many CZs over the years, and have used both 10, 15, and 16 round magazines. I've had a few 15- and 16-round mag springs fail (a very few), but I've never had any 10-round mag springs fail, and they all used the same springs!! (I shot a lot of IDPA for a number of years, and 10-rounders are the mag limit for Stock Service Pistol and Enhanced Service Pistol classes, and I used a lot of 10-rounders.)
If cycling is all that matters, why does the spring in a 10-round magazine outlast the spring in a 15 or 16 round magazine. It's is often the same spring!
The larger magazine is cycling less frequently for the same number of rounds fired!! (I used to think it was because the 15-round magazine was having to lift the larger stack of ammo up, but several engineers involved in this discussion on other forums explained that it was how far the metal was being compressed that made the real difference.)
I'll include a link to some mag springs tests below that you can examine, where spring strength decline despite only limited cycling. I'll agree that COMPRESSING the spring can damage it, if it's compressed too far (or too close to it's design limits), but wonder why reducing the depth of compression causes damage?
The experts will tell you that it's NOT the number of cycles that are critical, but the depth of the cycles that matter. In effect if, when cycling, the spring is never pushed past it's design limits, it can outlive the gun owner. If you push it too deeply (and some magazines are designed that way on purpose), the springs won't last nearly as long. v
Fatigue , which you mention above, is a type of metal deterioration. Wikipedia addresses the other factors that affect spring steels (and other materials), too:
http://en.wikipedia.org/wiki/Elasticity_(physics) http://en.wikipedia.org/wiki/Plasticity_(physics) http://en.wikipedia.org/wiki/Viscoelasticity http://en.wikipedia.org/wiki/Creep_(deformation) Viscoelasticity is very much at play in gun springs, creep less so.
If you talk with a metallurgist or someone who specifies springs for a work applications, many of them will tell you that the closer you get to the spring's elastic/design limit, the shorter it's life will be. But, if the design (or the device in which it's used) allows the spring to be used without getting close to that limit, there will be enough "spring" there to last a long, long time. That's why valve springs can cycles for many millions of times in an auto engine without breaking. It's not just because they're made of good materials – they're also not allowed to be compressed near their elastic limits.
The Firing Line, a forum I visit frequently, was down today, but hopefully will be back up tomorrow. The following information was posted by a moderator there. Hopefully, it'll be back up tomorrow. The following is a part of a much longer discussion on this stame topic, and addresses the tests that a member there conducted by
John Ksa (his 'net name). John is an engineer and very familiar with firearms, their springs, and interestingly, with spring-powered air guns. The following link is to a two-year test he conducted that shows measurable spring degradation for both Ruger and Glock springs over that period. That said, the springs continued to function properly, but they did degrade. They were cycled only once a month or so, to test spring strength change.
http://thefiringline.com/forums/showthread.php?t=538773&highlight=mag+springs The following comments by
John Ksa are excerpted from that link:
I won't rehash the topic because the information is there in the archives, BUT...here's some additional information.
On 21 December, 2013, I went shooting with some friends.
One of my friends brought along a Colt Government .380 which she only rarely shoots but which she leaves fully loaded at all times for self-defense. The magazines used were Colt factory mags.
She had consistent failures to chamber the last round from the magazine (all magazines) and she noted that this was a new development.
Here’s a gun that has been shot very little, but that has been left with the magazines fully loaded for a number of years. The magazines, which all used to work perfectly are now all consistently failing to feed on the the last round.
What’s particularly interesting about this situation is that the magazines are all factory parts from a quality manufacturer and also that they’re single-column magazines. Based on my informal research, it seems that single-column magazines are considerably less likely to experience this kind of problem. This situation proves that even if they are more resistant to weakened springs from extended periods left loaded, single column magazines are not totally immune to the problem.
I considered telling her that magazine springs never wear out from simply being left loaded since I hear it so often on the internet. I figured she would probably rather have some advice on how to solve the problem instead.
I gave her my standard advice about leaving magazines loaded.
Check your equipment regularly (we're all doing this anyway. Right?). If you note springs weakening from being left loaded, replace them with high-quality parts--first you want to eliminate the possibility of quality issues. If they weaken again from being left loaded, replace the springs again but now you've determined that even quality springs are likely going to weaken in your magazine design if left fully loaded for long periods. You have two options at this point. You can either underload the mags by a round or two or you can determine how long the springs will last and simply replace them before they weaken enough to cause malfunctions. Mag springs are cheap, even the best ones.
It is worth pointing out that not all magazine springs weaken from being left loaded. In fact, it's pretty uncommon. But it can happen and we need to be aware of the possibility so it doesn't take us by surprise. It's one thing to find weak magazine springs at the range or during a routine check. It's another thing entirely to discover the problem during a self-defense encounter.
