I’m going to add my two cents to this opinion (found via Insty, thankee) about keeping your magazines loaded:
Even when kept fully compressed, a magazine spring will retain its energy long past the operational life of the ammunition.
Here’s my take. I own dozens of magazines, of all types and calibers, fitting all sorts of guns, and I’ve owned most of my Chip McCormick (CMC) 1911 PowerMags for close to twenty years. I keep all of them loaded, all the time. When I was cleaning out my house, I found a box of what I first thought was junk (but wasn’t). At the very bottom, underneath all sorts of stuff like photos and old papers were two 10-round CMC Powermags, loaded. Judging from the other stuff in the box, I packed it when we lived in suburban Chicago back in the late 1990s, and had never fired the two mags — for twenty years.
With some trepidation, I unloaded them, expecting to find that the last couple of rounds were loose in the magazines — i.e. that the springs had “taken a set” when loaded to capacity and lost their tension. In both mags, the bottom cartridges were held as tightly against the mag lips as the first round. So I reloaded them.
The next time I went to the range, I fired off both mags through the Springfield 1911. Both mags and ammo functioned flawlessly. I put another ten loads of “new” .45 ACP through each (200 rounds in total) and the mags again worked as though I’d just unwrapped them.
The same has been true of every single magazine I’ve ever owned. The only time I’ve ever had an issue with a magazine was a cheap one that came with a Taurus .380 pistol — the “second” mag, not the one actually in the gun — and I think it was broken from the start. Magazine, say hello to Mr. Hammer.
As I said earlier: all my magazines are loaded, all the time. An unloaded magazine is just a box with a spring inside, just as an unloaded gun is just a heavy (and expensive) cosh. Whether they’re .22 LR mags for my Marlin 880SQ rifle, the Mec-Gars for the Browning Hi-Power or the many CMC PowerMags, if I pick one up or take it out of the bag, it’s ready to go. Even the several AK-47 mags that were tragically lost along with the gun in that canoeing accident were kept loaded. (As an aside, the mags that absolutely MUST be kept loaded are those that would be needed for your carry- or SHTF guns.)
That has been my experience, and that is my advice. YMMV.