Caliber
.40 S&W
The law-enforcement standard for decades — .40 S&W guns, recoil, and the 9mm debate.
About .40 S&W
The .40 S&W was developed to give law enforcement more punch than 9mm in a cartridge that fit standard-size pistols, and for two decades it was the dominant police round. It hits a little harder than 9mm and, right now, used .40 pistols and ammo are often bargains as agencies transition back to 9mm.
The downsides are real: snappier, more abrupt recoil that slows follow-ups, slightly lower capacity, and more wear on guns. Since modern 9mm performs to the same standard with less recoil and cost, .40 makes the most sense if you find a great deal and genuinely shoot it well. It's far from dead — just no longer the obvious default.