A (warning) graphic FBI PowerPoint presentation about the limitations of .40 S&W ammunition. A Pennsylvania police department has two conflicts where ten or more .40 S&W rounds fail to incapacitate the bad guy. The penetration was only 1 inch.
The officers credited their 5.56mm firearms with conflict resolution. Brick Oven recommends 7.62-39 rounds for conflict resolution* instead of the 5.56mm. They are cheaper and bigger.
* ‘conflict’ meaning self-defense