Consider the following:
- Your objective is to stay unhurt, and if you have to shoot, you have to stop an attacker, one way or another. The consequences of failure are apt to be severe.
- The human body is not a water jug or a steel plate. One has to hit small, parts of the body to do any good. Those parts are small, hidden, and moving. Hitting any of them is only partly a matter of skill; a lot depends on probability. More shots improves the odds.
- Forget about stopping power". You need penetration and expansion.
- You will not have the luxury of time for careful aiming. You will have to draw and fire very rapidly. The classic Tueller "drill" gives you a second and a half for the first shot Relying on that one shot would be like filling an inside straight.
- You should have the skill to land all of your hits in, say, the upper chest area of a target moving at five meters per second, firing fast--but under stress, you will likely not do so under stress.
- One shot could suffice, or two, or maybe three, but if that doesn't happen, you will not know about it until you have fired more. There will be no time for pausing to assess. That's why LEOs are trained to shoot until the threat goes down.
- The idea of reloading in the time of a heartbeat without looking at the gun the midst of a sudden attack is, for most people, a pipe dream.
Don't rely on my opinion here. Figure things out for yourself.
Consider how an attack would likely unfold, and contrast the necessary response with shooting at a stationary target at the square range at a rate of one per shot per second.
Consider what it takes to stop an attacker. Study the human anatomy. Massad Ayoob recommends buying a copy of
Gray's Anatomy handy, studying it, and keeping it handy for reference.
By all means, read, and reread,
Handgun Wounding Factors and Effectiveness, by FBI Special Agent Urey Patrick.
Bask in the day, Colt used to emphasize "that all important sixth shot" when competing with Smith and Wesson. Ads touted "20% more capacity". But when it comes to evaluating the how many may be needed, statistics don't work that way. Should any shots fail to hit effectively, six are more than 20% more likely to suffice than five.
The analysis linked below illustrates why that is true. Study it, and insert your own assumptions. You will undoubtedly come to agree that up to some number,
More is better. You'll never know what you need until after the event is over.
Good luck.
How Many Rounds to Carry
By the way, John's calculations are necessarily somewhat over-simplified, and they are based on the assumption that the defender will know to stop shooting when the assailant has been stopped. As mentioned above, that is not a realistic assumption.