[Danke]

The theoretical rule on springs is that it is cycling them that fatigues them. Not leaving them compressed or tensioned.

The reality is though they will sack under load and the smaller the spring the easier that is to happen. So something like a torque wrench with a tiny spring needs to go back to zero after each use. Something like an airsoft magazine will on the clock the longer it's left.

Brand will play into the longevity of the spring also so you'll get the players saying I never unload my gear and never have problems vs. the others who do see an effect.

If you wanted to be scientific you could build a rig to test the springs in a few magazines, then load them for six months, and re-test them after.