T. O'Heir said:
And springs do not lose temper from being compressed. A flat spring can work harden at the bends through extensive use over a very long time, but that's all. Mag springs do not require periodic replacement. Nor will they "take a set" if a mag is left loaded.
Not always true. It depends upon how deeply a spring is compressed or stretched, and HOW LONG that level of compression/stretching continues. Some gun designs never push recoil or mag springs to their limits, and those springs will be fine. Others may not fare as well.
The next time you install a new recoil spring, measure the length of that spring at rest before it's installed, and then use the gun for a while, and take it out and measure it again, at rest. It'll be shorter. That's called "taking a set." It'll generally happen pretty quickly, if the gun is cycled at all. It'll happen pretty quickly with mag springs, too... and happen more quickly if they're left fully loaded.
Wolff Springs has an interesting article about this on their FAQ page. If a spring is pushed to, near, or beyond it's design limit (generally called it's
elastic limit), it will degrade, and will often degrade quickly. Most gun designs don't push the springs that far. Wolff recommends downloading hi-cap mags a round or two
for long-term storage, but I suspect they are, like you, making a general statement that doesn't apply for all hi-cap mags. It certainly doesn't hurt the mag springs to download them for long-term storage.
I've had some unpleasant experiences with 7- and 8-round Kahr mags left fully loaded. Some of these smaller gun mags are, in effect, the equivalent of hi-cap mags in terms of the work required of their mag or recoil springs.
We've had this discussion here many times here on The Firing Line. JohnKSa, a staff member, an engineer, air gun and handgun enthusiast, and someone willing to do more than TALK bout the issue, did the following tests. Tell him that springs don't degrade. (His tests show that they can degrade, but won't necessarily stop functioning.)
https://thefiringline.com/forums/showthread.php?p=6005156#post6005156
The NEGATIVE example that always comes to mind is the recoil spring in the Rohrbaguh R9, the smallest 9mm available. (Rohrbaugh has since been bought by Remington.) The R9's recoil spring has a recommended service life of 250 cycles. Other recoil springs last a lot longer -- but because the R9's spring must do the same work as a full-size spring in a smaller area, using less metal, it doesn't last as long. Springs in a 7-round 1911 mag may last forever if the mag is left fully loaded (because there is a lot of reserve in that spring/mag design); springs in a fully-loaded 18+ round 9mm mag might not fare as well. Ditto recoil springs in some guns.
For most guns, it's probably a non-issue, but for some models, magazine and recoil springs CAN deteriorate pretty quickly -- depending on how the gun is used, and the gun's design.