I have some CMI M14 Magazines mainly 20 round magazines and a few 25 round magazines. Would there be any issues keeping these stored loaded? I know keeping AR Magazines stored loaded has no adverse impact on the magazine springs, but what about M14 magazines?

All my 10s and 20s are kept loaded. No problems. CMI sells spare springs, which you should have anyway.

Move this to GD if you want a real answer

No need to be an a-hole about it.

There are different possibilities for the metallurgy.

I took some loaded mags to the range Wednesday and they all fired fine with no issues. Best I can recall they have been loaded somewhere between 5-7 years.

Yes, there likely will be issues storing music-wire springs in a loaded condition for weeks, months or years

Evaluation of Pretreatment Processes and Long-Term Storage on Magazine Spring for the M14 7.62mm Rifle

No human-made spring is completely immune to a gradual loss of free length (and thus, load) while being stored compressed.  Stainless steels are the best, music wire is one of the worst.

Anyone who owns a tape measure can observe this in only a few weeks.

Lol, stainless steels typically don’t have enough ferrous metal to temper for springs.  Silicone steel is what most mag springs are made of and they lose very little under compression.  That allowance is typically engineered into the mags too.

Glock magazine springs are some sort of austenitic stainless, probably 302, which is a common material for springs.  Most of the springs in the AR15 are 17-7ph, another type of stainless.  Both of these materials have good stress-relaxation characteristics at room temperature.  The rate of relaxation (loss of free length) is very low, or practically zero for 17-7.

The Mil-Spec material for the M14 magazines spring is Music Wire per ASTM A228.  The complete TDP for this weapon is available at DefCad.  The CMI spring is apparently also music wire.  Music Wire doesn't have any allowing elements that restrict creep or stress relaxation, and anyone who owns a tape measure can measure the loss of free length of a maximally-stressed (which it certainly is) music wire spring.  Leaving it loaded for an indefinite period of time is foolish.

Any spring loses some free length in compression from new to “set”.  The tape will show that compression on any mag, but if the spring is designed with the set compression in mind, it’s serviceable with that compression.  I take it MP 38/40 mags are music wire springs and some of those have been fired off after being stored for 70 plus years fully loaded. Ive had zero feeding issues firing off CMI and Vietnam era M14 mags that have been stored fully loaded over 10 years.  Measure a shotgun tube mag spring before and 6 months after install with zero rounds through the gun.  It loses some free length just being installed.