I know the exhaustive FBI handgun report that came out a few years ago stressed the importance of quick, accurate follow up shots. They came to the conclusion that “stopping power” is a myth. There is no actual significant difference between a 9mm, .40 cal and .45 in terms of “stopping power”. Medical personnel cannot tell the difference between wound channels made with these various calibers. They also documented dozens of reports from the field of bad guys who kept coming and shooting after being hit center mass with a .40 or .45 cal. Thus, they concluded that the most important factor in the field is the ability to put multiple rounds in the target in as short a time as possible. Their range tests showed that their agents, both the best shooters and the average, were able to accomplish faster, more accurate follow up shots with a 9mm than the other two calibers. This is why the FBI is going back to 9mm.
Exactly. A facial surgeon who is also a member of my gun club confirmed this fact to me in a very interesting conversation.