Fatigue in a magazine spring comes from use, not static storage. I personally have used loaded 1911 magazines that were over 20 years old with no feed issues or failures. As long as the physical condition of the spring (rust or damage) is serviceable, you should have no problems. In your case, I'd be more concerned with storing the rifle in the hardshell box most of the time. Foam can hold moisture, and I don't leave my rifles in the case any longer than I have to. I usually spray Corrosion X onto a towel, then fold the towel around the rifle while in the case.
Your mileage may vary.... just my 2 cents worth...
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USMC 8652, 2531, RVN Jun '67, - May 69
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