What Deep Sea is noting is probably one of the most important things to remember, especially if you are regularly unloading/loading your weapon. Rotate and inspect those bullets regularly! I had two Corbon 10mm hunting loads that I had to dispose of recently because the bullets had recessed deeper into the casing after only 3-5 times of loading them into the weapon. Even more amazing was the fact that the bullets were crimped into the casing to prevent that from happening. I hate to think what would have happened if I had tried to fire them.
After like 4 years I think this dilemma has been resolved. :D
With any luck the OP will have a mag that he loaded when he posted this so we can get a nearly 6 year update on how it's working.
I would be curious about that (same round at top of mag) since I have heard the same thing.
As far as wearing out a magazine by keeping it fully loaded. I certainly hope not, because I have almost all of my magazines (AR, SIGPRO 40 Cal,
SW99 9mm and Sig Mosquito) topped off and ready to go if necessary. I do worry about the Mosquito just because of people talking about feeding problems withthat particular weapon.
I have kept both of mine fully loaded with no issues. I have seen magazine issues with 1911 mags at my gun clubs rentals where the spring weakens and the last round jambs. For the two weapons I own a Ruger 9mm and S&W .40, never had an issue.
I keep rifle mags as well as handgun mags filled at all times with no problems. I don't see any sense in not filling them completely or not leaving them filled for long periods of time.
What I was told by a spring guru is that the springs are fine compressed it is the constant compression and depression of them that can weaken them a little.. He also says that the springs are designed to compress pass the point of the amound of ammo by a couple more rounds worth of pressure... Im not sure, its a good question, I keep mine loaded but im gonna get extra and leave them empty just to be safe