Fit each empty magazine & draw the slide sharply to the rear as if firing. Look into the ejection port & notice how the slide stop is engaged by the magazine follower. It should be pretty obvious. Now do it with your ammo in magazine. If the ammunition contacts the slide stop, the slide stop may activate. A weak magazine spring may allow a cartridge to work forward under recoil, possibly activating the slide stop. It's actually pretty rare as spring quality is very good but magazines left loaded for long periods may lose their strength.
When I was trained, it was standard to rotate magazines periodically, rather than leave all loaded. It requires buying spare magazines.

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NRA LIFE
Reserve Officer 9yrs