What typically causes PMags to get retired? Obviously, driving over them with a truck would be a problem. Dropping them on the feed lips could be a problem. Beyond damage and accident, what does a PMag (or other mag) dying of "natural causes" look like?
Do feed lips get worn out? Do followers get worn out? How much does that depend on the amount of sandbox sand that's in them, versus just unavoidable wear from the brass sliding out?
Springs fatigue? Springs are replaceable. Would it make any sense to hoard some fresh ones?
I'm familiar with people updating aluminum mags with improved followers and perhaps fresh (or "extra power") springs, but it seems like that's as much about the design change as renewal, much of the time. On current-production M3 PMags, there doesn't seem to be much upgrading to do. Will springs and followers wear out before bodies?
How many rounds can someone typically put through PMags before they are toast?
And all the same questions for aluminum mags, too, I guess.