Spring, sproing, set, etc.
This topic will probably come up every so often as long as we use springs. And the accepted wisdom of the day has changed, as has the quality of the springs.
I have a few guns nearing the century mark, with original springs, and they work just fine. For them, I follow the rule taught me by my Grandfather. Never leave a spring under tension that you don't have to. The other main rule was don't dry fire (snap) the gun unless you have to. His primary gun was an Ithaca double barrel 12ga, stocked and choked (full and Full) to his specifications. It also has a third position on the safety, which allows the gun to be uncocked without dry firing. I have that gun, which turns 100 in two years. Works great. Incidentally, one of the selling points of that shotgun was that the springs were guaranteed never to take a set. I have a letter from Ithaca to my grandfather, dated 1949 reaffirming the guarantee on the springs. Never. And they meant it. Ithaca is gone, but those springs are still fine.
Leaf springs, especially old leaf springs are the ones most commonly found to take a "set". Coil springs seldom do, but seldom is not never. But, remember, springs do shorten and weaken with use. For good quality springs, the amount of use before this becomes a problem is considerably greater that ever in the past, way beyond the average use of a lifetime.
For about half my life, the accepted wisdom was "Don't leave mags loaded", today it seems to be "Doesn't matter". I would say, the best practice is what you feel comfortable with. Myself, if the gun (or mag) was made before say, 1950, I don't leave them loaded. Why risk it? On the other hand, modern springs, both in metal composition and heat treating are better than old ones.
I have heard of a couple of long term examples, (from sources I trust) but they are anecdotal, and I cannot provide any verifiable details. One was a 1911A1 .45, found after nearly 40 years, fully loaded cocked and locked, in a dresser drawer. The gun, and the loaded magazine both functioned properly when fired. Another one is a few years back, an MP 40 German SMG was found inside a wall in a Dutch (or Belgian) house, along with several loaded mags. Again, the gun and mags were reported to work fine when fired.
From personal experience, when I recovered some of my father's guns after his death, his 1911A1 had been in his dresser drawer, apparently untouched for several years. Not sure exactly how long, more than 5, but less than 20 years for certain. The gun was "gummy", and when I released the slide after clearing it, the slide only went about an inch forward, then stopped. He had 4 or 5 loaded mags with the gun. I did not fire them, so I can't say for certain if they would have worked, but I think they would have. I unloaded them, and a few weeks later, when I got everything to my home on the other side of the country, those mags, reloaded, have worked fine. And still do, years later.
I am conducting my own experiment, I took a few mags for a Tec 9 and loaded them up about 3 years ago. I'll shoot one in a couple of years, to see what, it anything has happened to the spring.
Today spring makers and spring(metal) experts generally agree that springs don't wear out from being held compressed, but wear out from cycling (compressed, uncompressed, compressed, etc), so I would have no worries about leaving modern pistol mags loaded for a few months, or even a couple of years. That said, if it is something you are going to trust your life to, then I would err on the side of caution.
