How long do you keep your magazines loaded for?  Is there a safe amount of time until i should empty them?

I read somewhere that you can keep military loaded mags loaded indefinately... Don't know how true that is.

The springs will weaken more by loading unloading (loading & shooting) than by leaving a mag full.

I've heard stories of mags loaded for 30 years and shooting just fine all that time later.

Mostly load them the night before, but my carry item has its mag loaded for about 10 years and it still functions flawlessly.

For best results, apply this logic to 30 rounders only. I have heard stories of 20s firing flawlessly after left loaded for decades, but they have a thinner feedlip design and are more prone to warpage. I load my 30s and seal them in cans. I seal my 20s unloaded.

Unless a spring is overstressed, flexing it will cause more "wear" than leaveing it as it is.

From the Ammo Oracle
http://www.ammo-oracle.com/body.htm#seal

"Q. Can I store ammo pre-loaded in magazines for an extended period of time?  Won't the magazine springs wear out and cause feeding problems?  Shouldn't I rotate my mags?

Shouldn't be a problem;

No and;

Probably not.

What wears out springs are cycles of compression and expansion and also over-compression.  So, every time you "rotate" your mags, you are causing additional wear by cycling the spring.  Loading and unloading magazines will cause more problems than loading and storing them for good.  For best results USGI magazines are probably the best bet because many aftermarket magazines use cheap springs.

One AR15.com member reportedly discovered a fully loaded 20 round USGI mag that was loaded in the Vietnam era.  20 some years later it not only functioned fine but continues to do so.  Others have reported 1911 mags and Luger mags loaded up since World War II that continued to function perfectly when first fired after 40 years".

Read all about ammo at: http://www.ammo-oracle.com

I came upon four mags over the holidays (2-20's and 2-30's) that were probably fully loaded for about 10 to 15 years minimum...possibly up to 20 years.  They were all colt mags with alloy followers. I dumped all 100 rounds flawlessly.