Handgun rounds are - ineffective fight stoppers!
Have a plan A, then have plan B ready for when your chosen "magical/one-shot stopper/ultimate defensive round/etc.." does not work as advertised.
My plan A: 2-4 accurate/quick rounds to center mass, if that has not stopped the threat, plan B is a head zone shot.
This of course is subject to change - after all, gunfights do not always go as we plan.
Tomorrow's battle is won during today's practice.