A lot of gun owners worry about their gun going “click” instead of “bang.” Yes, well, with basic maintenance and self-defense (i.e. hollow-point) ammo, the vast majority of modern handguns are incredibly reliable. As long as you test fire your gun and ammo on a regular basis, you have little cause for concern. That said, the desire to reduce the odds of a life-ending mechanical malfunction is perfectly understandable. The single most likely cause of failure . . .
The ammunition magazine. The usual justification for carrying a spare ammunition magazine: more bullets! Fair enough. But given that the average gunfight is three rounds in three seconds at three yards, there’s an even more important reason: a Plan B if Mag A fails.
That’s why so many manufacturers spend so much money creating reliable magazines, and the aftermarket for high-quality magazines is so robust: gun and mag makers know gun owners don’t want to have to use a Plan B. It’s also why many gun buyers examine the sturdiness of a gun’s magazines before making their firearms selection.
Yeah it’s that important. Even so, sh*t happens. Mag lips (the top of the magazine) get bent. Dirt and other foreign substances find their way into magazines. Magazine springs lose their shove. In short, your ammunition magazine is much more likely to fail than the gun.
To hedge against a mag failure, examine your magazines on a regular basis. Look for foreign substances; make sure your mags are both clean and functional. Check for bent lips or any other damage. If a mag loads and unloads well, if it shoots reliably, you should be good to go.
It’s worth repeating: the gun range is best place to check your magazine/ammunition combo.
If you experience a magazine-related failure, try other similar magazines. If it’s a problem with one mag — where your other, similarly loaded magazines don’t fail — don’t carry the non-operational mag. (Mark an X on the bottom with a white Sharpie and set it aside for failure drills.) If all your mags fail, change ammo. If that doesn’t solve your problem, consult a gunsmith.
More than that, carry a spare magazine and practice on-the-fly magazine changes; including changing mags while moving. (You can do this at home with empty magazines and safety checked, unloaded firearm, not pulling the trigger.) There are magazine holders of various sorts, both for your pocket and your belt. Use one. Carry a spare ammunition magazine. Your life may depend on it.