Loaded mag spring test results:

[Kymasabe]

Well, I didn't intentionally perform a mag spring test to see if any of my mags springs weakened over time. No instrumentation was used for testing purposes.
I recently aquired a Savage model 1917 .32cal pistol (made in 1920) that was fired, cleaned, loaded and put in a drawer aproximately 30 years ago. Buried and forgotten until recently. A customer of mine found it while looking for something else and brought it out to me. Had been laying around so long, I couldn't drop the mag as the mag release was gummed up and stuck, as well as the slide, took forever to get the slide back to check the chamber, which turns out had a round in it that ejected when I finally got it open. I took the gun home, took it all apart, cleaned it lubed it, and a trip to the range impressed me. The old gun fired fine, cycled fine, no feeding, firing, or ejection problems at all. And there's a 1920's mag spring, compressed for 30 years and still working. I was shocked.
I can't believe that old gun was considered a pocket pistol way back then, weighs a ton by todays standards.

 

[Walt Sherrill]

Lots of guns with standard capacity mags (not greater capacities than are usual for a gun of the same size) function well when they have been kept loaded for many years. Tales about 1911s stored from WWII or before with loaded mags that later function properly, are common.

You get different stories and results when you try the same sort of thing with hi-cap mags (whether for a full-size gun or a sub-compact.) It seems worse, for some reason with double-stack mags that hold 15-18 rounds of 9mm, or larger-than-usual numbers of rounds in .40 and .45 guns.

 

[rust collector]

They were a pretty solid pistol. Have you checked out this site?
http://www.vintagepistols.com/1907/index.html

Hit the buttons in the bar.

 

[kragluver]

Assuming no corrosion effects, spring force degrades slowly with repetitive use - not significantly under static load.

 

[Walt Sherrill]

It depends on the nature of the static load.

If the mag spring is not compressed to its elastic limits, it will likely do well. If it's a hi-cap mag, and the spring is fully compressed, there can be problems, and failure over time.

(This is being discussed in great detail on another forum (The Firing Line), with several experts participating, and many links offered to technical sources as evidence.)

Check out the WOLFF Springs website FAQ for additional information.

Folks familiar with air guns will tell you, too, that it's long been known in the air gun sport that springs left fully compressed die an early death.

Many of the older guns have mags that never really push their springs that hard. Many of the newer designs use springs as though they can be easily replaced, and push the springs farther than once was the case.