According to statistics, most self-defense situations follow the “Rules of Threes,” meaning the fight will happen at 3 yards with three shots fired and last about three seconds. But, a gunfight is not a statistic, which is why most experts recommend training for a drawn out fight.
Of course, one requirement of a prolonged fight is ammo. If you only have the rounds that are in the gun, then you are limiting you ability to continue the engagement and had better have a backup plan for getting out of there.
Even service-size handguns can only hold so many rounds, and most of us carry more concealable handguns anyway that only hold between six and 10 rounds, depending on the caliber. My personal gun holds seven plus one rounds of .45 ACP, which means I have enough rounds for most situations, but I still carry a spare magazine that ups the ante to 15 rounds of flying ashtray ammunition.
Now, spare ammunition should be included in every self-defense plan from walking down the street to barricading oneself in a bedroom while waiting on the police to respond. Today’s tactical shotguns can be fitted with shell holders, AR magazines can be attached together and there are numerous pouches for carrying a spare magazines or speed loaders, such as these from CrossBreed and Galco. Of course, you can also rely on a New York Reload. Personally, I prefer to cover all the bases.