Smith & Wesson and Winchester introduced the .40 S&W in 1990 to replace the 10mm cartridge which had been used for a short time by the Federal Bureau of Investigation. The 10mm had proven to be too difficult for many agents to control when firing due to the combination of harsh recoil and large grip size. In response, the FBI searched for a cartridge with less recoil that fit in existing 9mm frames and could deliver the amount of penetration required by the FBI. The .40 S&W met these requirements, was adopted by the FBI, and enthusiastically embraced by the law enforcement community. Civilians soon followed and offered their own endorsement of the caliber.
A strong feature of this ammunition is that it is a "middle ground cartridge," yet it avoids being a compromise. The .40 S&W has more muzzle energy and down range energy than a 9mm, although the same sized pistol in 9mm will be able to hold more rounds since the 9mm cartridge is smaller. A pistol chambered in .40 can hold more rounds than it could of .45 ACP, but the muzzle energy of the .45 is considerably higher than that of a .40. The .40 strikes the right balance between muzzle energies and magazine capacity, and has been approved by exhaustive testing on the part of the FBI and many other agencies. The result has been wide-spread adoption of the .40 among the police community. It is also worth noting that the .40 S&W has been adopted by the US Coast Guard as its primary issue sidearm.
The .40 is popular with civilians for many reasons. A wide variety of options exists for bullet weight and bullet design, and if a manufacturer produces a new line of self-defense firearms, they are sure to offer it in .40 caliber. Civilians appreciate the same benefits of the caliber that made it so popular with law enforcement: magazine capacity, muzzle energy and limited recoil. The cartridge is popular for home defense and concealed carry, as seen in the number of pistols chambered in .40 S&W of compact and sub-compact size. Defensive ammunition in .40 S&W is offered by several manufacturers including Federal, Hornady, and Magtech, just to name a few.