There are some truths and some misconceptions about the durability of pistol magazines. It would seem that everyone has an opinion, but most are based upon conjecture and not science.
The truth is that modern magazines and their related components are the best that they have ever been. Having said that, all officers must understand that magazines are mechanical devices and as such, are subject to wear, tear, and breakage. The weakest link in any semi automatic feeding system is the magazine. Most frequently issues with feeding reliability are as a direct result of spring tension within the magazine.
Magazines left loaded for long periods of time are subject to spring set, which equates to a lack of upward pressure on cartridges stored, as the weapon cycles. Having said all of that, I have found an easy fix that I teach my students. For any given pistol, I recommend ownership of a minimum of nine (9) magazines. Three will be carried daily, three will be at ‘rest’ left unloaded and three will be dedicated as range only magazines. I typically tell my students to mark the base plate of their range magazines with a dab of bright nail polish, so that the magazines that are dropped, kicked, stepped on and dirty never get mixed in with duty magazines. That leaves us with six additional magazines.
My recommendation is that when your duty ammunition is fired or turned in at requalification time, your fresh ammunition draw is then loaded in to the magazines that have remained empty during the last cycle. Then the magazines most recently left loaded are placed in a ‘rest’ mode until the next cycle. Over the last twenty plus years of firearm training, I have found this technique to be the very best at eliminating magazine issues.