Spring fatigue is caused by cycling loads (compression then decompression), however springs do have some creep effect (being loaded under a contant load) which is really small for steel springs much less than 1%..So keeping the mags loaded is OK. One time I was worried about spring loading and that's why I did some research on the topic..My 2 cents.
I wasn't aware of the opposing force (decompression) also playing a role in wearing out the springs. I suppose I should cut down on the 2-month "breathing" I do because I thought I was relieving some mag tension.
Back to the topic. Usually I have three weapons at home ready to go (my EDC via minivault and two in the main safe), each with a loaded mag next to it. If I can't stop a threat with that available firepower, I need to seriously consider evacuating the house, or pray....
I beg to differ not that the springs would gobad but would need a break. I may not have as mainy years with weapons as most on this site, but I have used mainy differant weapons from US to foreign, on active duty and personal time. I have had springs from the fallowing weapons systems that "loose pep in their step."
sig sp 2340
colt and FN m16 a2
most of my magazines where new except for about 3/4 of my 5.56 mags. i had to "relieve tension" from the mag springs because after being loaded for a while they would not cycle the rounds up into the chamber. So the armors had us take apart the mags and give the springs springs a break. It was common in the baretta mags not so much in th m16 but it did have to be done. my new duty weapon a sig sp 2340 is horible with it.
Granted over [I]years[I] springs do lose their spring but I think gun makers take this into account in their design process and build them to be fully loaded all the time and also to be cycled many times.
To store fully loaded mags over a long period of time will weaken the spring in my opinion, 6-7 months with a fully loaded Glock mag gave fedingproblems due to a weakened spring, when emptied it regained some strength.
Storing a loaded mag is absolutely no problem, there is two ways to do it as i see it:
* Use two mags to alternate between and move the bullets to the other mag every third month and the magsprings will live forever.
* Remove two bullets from the fully loaded mag, that way the spring will last very long time before the feeding problem shows up.