Can you inset full 30 rounds into a 30 round mag for long term storage without the spring weakening?  If the spring weakens with full capacity, how long does it take for the spring to weaken?

I don't worry about it.  Never had a problem.  I have some that I am 'long term testing' or whatever you want to call it.  About a dozen that have been loaded for 6-8 yrs.  Don't know when I'll shoot them, but hey, some day.   A couple of years hasn't hurt any I have used (did about 10 on that one).    Admittedly small samples, but I am happy.  All regular springs and old style followers.

Doc

Cool, thanks for the info