I found a thread/post in here before and couldn't find it in the search function. It is regarding the amount of ammo to hold in a CCW. The post mentioned that even trained LEO miss roughly 80% of the time, and with a 10 round mag, they would only get the perp twice. So with a 20 round mag, they would increase their chance to hitting the perp 4 times.
I am not sure how accurate those numbers are, but if anyone knows any info related to that (or could find the post) it would be of much help!!