Was it Bill Jordan who said (approximately) "If you don't get it done with the first six, six more probably won't help much"?
I think it was.
I also think it was FBI research that showed the typical shooting incident occurring at very close range, involving the expenditure of two or three rounds, and lasting something like five seconds.
As wiser guys than I have already said here, making those first shots good ones is more likely to save one's bacon than having fifteen more to use.
And of course the real first rule of gunfighting is "Stay out of gunfights."
"Don't let macho be your epitaph."