How Often Should You Replace Your Carry Ammunition?
Unlike stored ammunition, which will have a shelf life of many decades if kept dry and at a relatively low and stable temperature, carry ammunition, on average, should be changed at least twice per year. Consider the following:
Carry ammunition is subject to almost continual vibration. You put your gun on, you take it off, you walk, get in and out of chairs, get in and out of cars, etc. This jostling action on the propellant can degrade it over time.
When the gun is not on you, such as overnight, the ammunition reaches room temperature. When the gun is on you, the ammunition approaches or even reaches body temperature. This is especially the case when you carry inside the waistband, or in the winter, when you wear heavy clothing
When the gun is not on you, the ammunition is exposed to the ambient humidity. When the gun is on you, the ammunition is exposed to high humidity due to perspiration, especially if you are active.
Many people have to unload and reload their guns frequently, such as if you have to travel through a heathen state like Illinois, or if you have to go onto and off of a school property. If using a semi-auto, each ejection of the round from the chamber can damage the rim, potentially causing a future failure to eject when that round is fired, and each reinsertion into the chamber can degrade the friction seal between the bullet and the case, potentially moving the bullet further back into the case.
Carry ammunition is not inexpensive, but the cost of replacing it twice per year is nothing compared to the value of your life, which after all, is why you carry. A twice per year change is standard for may law enforcement agencies; you should do the same.