Does leaving my magazines loaded damage the springs or cause warpage in plastic mags?

No it does not damage the spring. I watched a good video on this one day about how it's spring steel and it will always hold it's original shape.

Lots of talk about that around here. Many guys are in the camp of leaving a mag loaded does not hurt them. Exercising them, load, use, load, use is what makes springs degrade.

My work mags stay loaded for 6 months or so before we shoot and change out our duty ammo. 5 years with same mags.

Yes I shoot way more than that. I have range mags so I’m not constantly downloading my duty ammo.

This is what I believe when I thought about it using my engineering hat.

As for warpage, i assume you mean as it swells side to side. I think this is only an issue to double stack/staggered stacked magazine. This part I will believe will cause u issues, especially fully loaded. The double/staggered cases within the magazine now have an internally applied force laterally, meaning it causes the magazine to swell side ways. Because they are staggered and cases are circular profiles, the geometry of how the rounds set will apply a lateral/swell force as a component of the spring force pushing up. So IF you fully compress the spring, then the spring force is the greatest at its most compressed(spring force = spring constant x displacement). Which also means the force applied by the cases within the magazine is at its greatest. This does NOT happen in single stack mags, like the aics for bolt guns, because their is no resultsing later force as the spring pushes up.

FYI, i have a 6.5 grendle mag, the e-Landers metal one. The mag is based 2 plates held together with by stamping. it came apart at the seem. Try fully loading an ar and feel how much it swells.

Now I have no idea is this actually damages mags long term, but again I had a magazine with a failure in the swelling/lateral direction.

Not an issue.