9MM RESURGENCE: Why the FBI & Police Went Back. “The reality is there is such a minute difference in the terminal performance between the 9mm, .40 S&W and .45 ACP, that the interface between the shooter and the handgun, ammunition capacity and shot placement (accuracy) matter more. It would seem it has taken bullet engineers about 30 years to level the playing field between these cartridges, and it has taken the FBI about the same amount of time to realize the obvious.”

Well, the FBI.