While there is evidence that ammo kept in your handgun can and will function for decades if stored in non-extreme conditions...There are some reasons to swap it out for fresh ammo routinely. Here’s why:
1. Repeatedly chambering/unchambering a round can cause the bullet to push back into the case, thereby increasing the internal pressure of the cartridge if it’s fired. In turn, an increase in pressure can at best cause accuracy to deviate, but at worse it can cause a major malfunction. Bullets are “seated” into shellcases when loaded at the factory, but bullets are not permanently fixed in place. After all, the bullet must separate from the case when it is fired.
A few chamberings may not cause the bullet to become pushed into the shellcase, but over time the repeated forces involved in chambering the round several times can unseat the bullet.
There are two remedies: First, if you chamber and unchamber your carry gun daily, rotate the rounds in the magazine so you don’t “pick” on one round—repeatedly chambering the same round several times. Oftentimes, the round on top of the magazine gets re-chambered multiple times—thereby increasing its chances of push back.
Secondly, occasionally check the overall length of the cartridges in your concealed carry gun’s magazine(s) by removing each cartridge and comparing them to a control group, using a brand-new cartridge of the exact same make. Visually inspect all of the cartridges on a flat surface nearby the new cartridge, and/or lay a straight edge over them to make sure none are notably shorter. If you find one that is, discontinue its use.
2. No matter where you keep your handgun and spare magazine(s), eventually they’re bound to become fouled with lint and grime. Lint from pockets, purses, bags, consoles, etc. seep into tight places, even gun chambers. Lint soaks up lubricants that will dry out guns that need to remain slick and rust free; lint mixed with moisture will also gum-up springs and metal parts vital to your handgun’s proper functioning. So once per month, inspect (by unloading) both your gun and its magazines for lint. Clean as necessary.
3. While ammo is proven to last for decades if kept in controlled conditions, be on the safe side by refreshing the ammo in your concealed carry gun each year. A fun way to help you remember to do it is to shoot all the ammo in the magazines of your personal defense guns each New Year’s Day. It also makes for great practice with your defensive ammo. Then, reload with new Winchester ammo and prepare for the next year of dedicated, safe and responsible carry.