10mmAny newer shooter should think twice before deciding to carry a gun chambered in this hard-hitting caliber. What am I talking here? Back in the 80s, the FBI switched from 9mm to 10mm. Their reasoning was because the NATO round didn't have the ballistics needed to stop the bad guys (back then, the parabellum was insufficient as a man-stopper, unlike today's technologically advanced rounds are).
Well, after they switched, they found that a lot of their agents were inaccurate shooters with the 10mm, and were eventually forced switch over to the 40 S&W, which was a compromise between the two.