Almost everything on earth eventually deteriorates to a point where it is no longer useful or even safe to use (except for honey): ammunition is no exception. How long your ammunition lasts depends a lot on how it is stored. Yes, I’ve heard stories of Vietnam, Korea and even WWII surplus ammo that still functioned, but I certainly wouldn’t suggest trying that a home. I recently came into some 22LR ammunition that was still sealed in its factory packaging and had been stored in a bedroom closet for about 30 years; I experienced an over 30% fail rate with this ammunition. Not good.
Modern firearms ammunition is manufactured with an expected life of 10 years, if protected from extreme heat or moisture. That life expectancy can be extended by storing in a cool dry place. I’ve been told, though I have no way of proving it, that vacuum sealing it will extend its life even further. Bottom line: if you store it properly, it will probably out live you.
So keeping all this in mind, think about the defensive ammo in your carry weapon and when was the last time you changed it out? Those expensive hollow points you have in your carry gun are exposed to the same elements you are; rain, snow, cold, damp, etc. If you leave a gun in your car it is exposed to cold, damp and extreme heat. Due to these factors it is recommended that you replace it at least once a year if not more. Yes, it can expensive to replace those hydroshocks you spent $35 on, but how expensive would a failure be in a crisis situation? Keep your powder dry!
Hope for the best, prepare for the worst.