Over the years I, like all shooters, have heard theories on magazine springs and how to treat them. A few years back I took a tour of the Sandia National Laboratories and I spoke with a metallurgist who was also a shooter and he had some noteworthy insight on the issue. As he said, “if the spring was made of the right materials and heat treated properly, leaving it loaded will not cause the spring to weaken.” Leaving a spring compressed will not weaken it, it is compressing and relieving the spring a lot that causes them to weaken through use. He added that any failings are usually due to poor materials or bad heat treating.
This is yet another reason to buy only the best. If you have magazines of questionable manufacture it may be worthwhile to stock some spare magazine springs at the very least. Wolff, Wilson and others make quality springs for this purpose.
Ever since my conversation with the man at Sandia I always got a kick out of hearing about people who rotate their magazines “so the springs can rest”. Never made sense before that, steel does not rest and recover like muscle tissue, but hearing the science behind it was an education. Same with downloading magazines a round or two. It won’t save the spring any (but it will make the bolt/slide strip the round out a bit easier but that should only be an issue if there are problems with that weapon.) If you want to rotate your magazines by running rounds through the gun that is great. Practice is never wasted and it will field test those magazines.
One more word of warning is that you should never stretch magazine springs, this is at best a short term fix. They will weaken again, even faster than before. Replace them when they go bad, don’t stretch them out in hopes they will still give good service. – Jake at The Armory