I agree with Nukinfuts. I have see 2 clips in my life go bad and spring fly out and I mean that sucker comes out very quick and bullets go everywhere.
That's not a spring failure, that's a floorplate failure. They had to have been dropped too many times, or there was a flaw in the molding process that the spring took advantage of.
Personally, I leave them loaded except when I'm shooting, in which case they get worked. Specifically, whatever I'm carrying and usually one other gun have a standard duty load, three full mags plus one in the chamber, loaded. The rest of my mags for those guns and most or all of my other guns, are unloaded until they get a job. If it lives in the safe, it's unloaded and all of its mags are too.
Empty mags will not wear out as quickly as full mags, which won't wear out as quickly as mags that are worked regularly. I don't think leaving them empty or full will for long periods will make much difference. Loading and unloading them regularly is what will wear them out in a hurry.
I've taken 10 and even 15 year old mags in to Glock and left with the same spring because the armorer felt it was still good.
I had to replace my mag springs in all three mags for my Walther P99. It was only two years old when I got it, but I don't know the history for those two years, so I can't say why they failed.
Aside from that, the only magazine springs I've ever had to replace were in my .25. They sat loaded for 10 years or so...it went into the safe and just stayed there until I decided I needed to check it out. ALL of the springs in the gun had failed. Both mags, recoil, even the sear spring was weak. I'm not sure how old the gun is, so I don't know how old those springs were, but I'd put them at 15-20 years old. The original manufacturer is defunct and another company owns the name. Thankfully they support the gun! $15 in springs and two new mags later, it shoots like new.
