Is it okay to leave a magazine fully loaded for extended periods of time?

I have some home defense rounds that I was planning on leaving in a second magazine. These are expensive cartridges so I don't plan on firing them until necessary. Is it okay to leave the magazine fully loaded for many years?

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good information to know thanks

Thanks for the info. I was wondering if bullet tarnishing could be a potential problem as well

Ive googled this before too and as already mentioned, the concensus is it's the compression/release of springs that wears them out and not just long term compression. The caveat most people cite is whether or not the mag has metal feed lips since if they're not they could warp and cause feeding issues.  Like you my question involved home defense - I leave a couple of glock 21 mags loaded long term with more expensive JHPs that I don't use for practice. They have metal feed lips but I've had them in there for years so hopefully the concensus is correct! 

As far as my pmags for my ar10 and m4, I have ten mags for each but i leave all empty but one for my m4 because those weapons are not for what i call routine HD; in other words my glock and mossberg 500 are for routine home invasion type situations and my ar10 and m4 are for civil emergency type situations, like the aftermath a of hurricanes, earthquakes, zombie apocalypses, :0 etc - that's their application. If the shit hits the fan ill load them then. I just leave one m4 mag full just in case, but why take a chance on the unknown by keeping all 20 mags loaded?

Thanks for the info. I was wondering if bullet tarnishing could be a potential problem as well

this is more of a problem.
i only keep nickel plated self defense rounds loaded now. brass isnt as smooth feeding after sitting out in 70-80% humidity for awhile. i dont see it getting so oxidized they completely get stuck in the mag or the chamber, but i could imagine a misfeed or oob type of thing happening. especially because hollow points already dont feed as smoothly as a round nose.

strangely steel cased ammo hasnt visibly tarnished at all for me even after handling bullets with sweaty hands at the range then putting them back in my ammo can when i dont fire them all.

yeah mine are brass and darkly tarnished.  But popular thought is that so long as the primer is clean of oil or solvents, its just a cosmetic issue.  They're actually SJHPs but though early on most people thought glocks were sensitive to non ball ammo, most people don't have issues with running a variety of ammo through glocks.  I used to practice with them before ammo got expensive and never had issues.....but I guess I should burn those old rounds and get some new ones in there.

these for 10s and 20s but the idea is sound for any mag.  put in a dessicant pack too.






and of course there's always the good old ammo can.