I claim no special expertise. The state of spring metalurgy is pretty good. PMAGs have a cover which takes the tension off the lips and seals the mag from dirt. IMO, it's the best currently available and meant to be kept loaded. A Glock rep told me that he keeps his mags loaded for months at a time before he rests them. As someone else pointed out, an unloaded mag is not much use. I keep some of my Sig, AK, and AR mags loaded and I sleep better.