Springs take a set then stop when loaded.
Working the spring (loading/unloading) weakens the spring. Think of twisting a piece of baling wire. Bend it and it takes a set. Bend it back and forth and it’ll break.
I’ve still got a 20 round mag in my truck that’s been loaded with 18 rounds for 20 years or so. I’ve shot it and reloaded it a few times but it still works just fine.
The covers on Pmags are dust covers only.
