I have a rotation system: My birthday is in late May, and thanksgiving is in late Nov, which puts them conveniently 6 months apart, give or take a day or 2. That is when I "swap" mags (all are color coded) on all of the pistols I store loaded, whether it is a "carry" pistol or just something I keep handy and ready in the house. So the mags stay loaded for 6 months at a time and "rest" the other 6 months. The "unloaded" mags get used periodically during the "rest" phase for training at the range. Never had any issues doing this. My pistols that stay loaded and ready include several Glocks and a S&W shield, all using factory mags, and 1 1911 that I use Ed Brown mags in.