"Borrowed" From Rangemaster Tactical Talk Volume 11, Issue 10
Replacing Carry Ammunition
Some people call it “carry ammo”. Others call it “duty ammo” We are referring to the ammunition you actually carry in your handgun for self defense purposes, as opposed to “practice ammo”
Carry ammo should be shot up and replaced with fresh ammunition every six months. The ammunition you carry in your gun is exposed to extreme temperature variations, as you go from air conditioned office to summer outdoor heat, or warm cozy office to 25 – 30 degree winter outdoor weather. If your gun is left in your car in the summer, it is exposed to temperatures in excess of 140 – 150 degrees. Traces of gun oils and cleaning solvents inevitably get on the ammo. All of these things can lead to serious issues.
Ammo is relatively cheap. Shoot your carry ammo in a practice session and replace it with fresh ammo every few months to avoid this hazard.
On a related note, some people habitually unload their pistols when not carrying them. If you do this, take the round that came out of the chamber and put it aside, for later use in practice. Do not repeatedly load the same cartridge into your pistol. When the slide slams the top round in the magazine out of the magazine and onto the feed ramp, the bullet nose takes a pretty hard impact on the feed ramp as it is chambered. Repeatedly chambering the same round can pound the bullet deeper into the cartridge case, resulting in drastically higher pressures. I never chamber the same cartridge more than twice before replacing it. Ammunition is a perishable item. Carry ammo needs to be fresh and properly cared for.