JohnSKA had an excellent article or post on this.
The problem is the following:70% of shootings take place in dim light.
At combat ranges the accuracy of the CCW shooter is generally 30-50%.
Your chance of dual or triple attackers is very high, also in the 70% range.
Your chance of one shot stops with most CCW calibers isn't very good, either.
Glocks aren't legendary for accuracy considering the long, heavy first pull, and the shorter second pulls on the trigger, not to mention the rather weird trigger, altogether.
The bad guys don't shoot much better, and, they also generally don't carry calibers that really stop people, either. How much ammo they carry is another issue.
John pretty much convinced me that if I was carrying a revolver, I should either carry a backup, or a speed loader.
Likewise for autos, don't leave those flat, easy to conceal magazines at home.
If your hit rate is 3 of 10 in dim light, with 2-3 moving targets, the odds are in their favor if they are shooting at you.
So, you are at most likely to hit each guy with one shot, out of ten rounds, and, it's highly unlikely that one shot is going to stop the attacker.
I'd sure like a backup or more ammo.