The .40 S&W (10x22mm Smith & Wesson) is a rimlesspistolcartridge developed jointly by Winchester and Smith & Wesson, two famous American firearms manufacturers.  It uses .400-inch (10.16 mm) diameter bullets ranging in weight from 135 to 200 grains (9 g to 13 g) and operates at about 33,000 psi (230 MPa) pressure.
The .40 S&W cartridge debuted January 17, 1990 along with the new Smith & Wesson Model 4006 pistol, although it was several months before the pistols were available for purchase. The .40 S&W evolved from the 10 mm Auto pistol ammunition which had been adopted by the FBI, but turned out to be too powerful for some of the agents, and exhibited poor accuracy in rapid fire. The 10 mm Auto gave performance that overlapped with the lower end of .41 Magnum performance; the recoil and muzzle blast, especially from a short barrel, were found to be too much for many shooters. Essentially it was found that a pistol powerful enough for deer was not needed for the purpose of defense or law enforcement. The FBI started using reduced-charge version of 10 mm Auto ammunition, a subsonic load often referred to as the "FBI load" or "10 mm lite." Smith & Wesson redesigned the cartridge to make it shorter while maintaining the performance of the FBI load. They also decided to use a small pistol primer, rather than the large primer used for the 10 mm Auto. The .40 S&W cartridge quickly surpassed the 10 mm cartridge in popularity and units sold. With the .40 S&W being shorter than the 10 mm Auto and approximately the same length as the 9x19mm Parabellum cartridge, many existing 9 mm pistols could be easily adapted by their respective manufacturers to fire the new cartridge.
The case of the original 10 mm Auto had the same head dimensions as the old .30 Remington that was designed circa 1906 for the Remington Model 8 semi-auto deer rifle. The bullet was the same diameter as the old .38-40 dual use rifle/revolver round from the Old West. The .38-40, long obsolete, was known for good stopping power, and the .40 S&W reflects this, in a far more compact package.
Austrian manufacturer Glock beat Smith & Wesson to the dealer shelves in 1990, with pistols chambered in .40 S&W (the Glock 22 and 23) which were announced a week after the 4006. Glock's rapid introduction was aided by its engineering of a pistol chambered in 10 mm Auto, the Glock 20, only a short time earlier. Since the .40 S&W uses the same bore diameter and case head as the 10 mm Auto, it was merely a matter of adapting the 10 mm design to the shorter 9x19mm frames. While the Glock 20 was and still is considered an excellent pistol in 10 mm Auto, Template:Weasel-inline it has sold vastly fewer units than its .40 S&W cousins.
Initial acceptance of the .40 S&W was slow, since the round was considerably less powerful than the 10 mm Auto it was based on. This led to derogatory names such as ".40 Short and Wimpy" or ".40 Short and Weak."
The 40 S & W is dimensionally identical to the 10 mm Auto except for length. Both cartridges headspace on the mouth of the case. Thus in a semi-auto they are not interchangeable. Smith and Wesson does make a double action revolver that can fire either at will using moon clips. A single-action revolver in the 38-40 chambering can also be modified to fire the .40 or the 10 mm if it has an extra cylinder. The .40 will at short range take deer with loads that come close enough to the combination of .40 caliber or better, 200 grains (13 g) bullet or better, and 1,000 feet per second (300 m/s) or better. It is also suitable for small and medium game.
IMI attempted a similar cartridge in the 1980s, called the .41 Action Express (or .41 AE) for the Jericho 941 pistol. This cartridge was based on the .41 Magnum case, cut down to fit in a 9 mm frame, and using a rebated rim the same diameter as the 9 mm Luger. The .41 AE is ballistically similar to the .40 S&W, to the point that many reloading manuals suggest using .40 S&W load data in the .41 AE. The .41 AE is a more attractive cartridge in many ways, as the rebated rim allows a simple barrel and magazine change to allow most 9 mm guns to be converted to .41 AE. The .41 AE uses .410 inch bullets, whereas the .40 S&W uses .400 inch bullets. However, as it lacks the backing of ammunition manufacturers in making .410 caliber bullets suited to semiautomatic pistols, the .41 AE has not achieved widespread popularity.
The .40 S&W cartridge has become a huge success in the United States because, while possessing nearly identical accuracy, drift and drop, it adds 50% more energy over the 9 mm Parabellum with a more manageable recoil than the 10 mm Auto cartridge. In the rest of the world it has become a popular combat pistol shooting sports cartridge. With good JHP bullets in the more energetic loads (> 500 ft-lbs) the .40 S&W can create hydrostatic shock in human-sized living targets.
The energy of the .40 S&W exceeds all standard-pressure and +P 9x19mm Parabellum loadings and many standard-pressure .45 ACP rounds, generating between 450 and 600 foot-pounds (550 J and 800 J) of energy, depending on bullet weight, with mid to high 500 foot-pounds typical. Both the .40 S&W and the 9 mm Parabellum operate at a 35,000 psi (240 MPa) SAAMI maximum, compared to a 21,000 psi (150 MPa) maximum for .45 ACP. Some small ammunition manufacturers offer .40 S&W ammunition consistently developing energy well above 500 ft·lbf (700 J) in all their .40 S&W ammo as off-the-shelf items.. While SAAMI has not established a +P standard for the .40 S&W, there are companies marketing ammunition claimed to be +P, but they do not provide pressure data to support +P labeling.
The .40 S&W is considered by some the best cartridge for law enforcement use available today, combining superior stopping power when using expanding ammunition and manageable recoil in a package that remains compact, even when using a double-stack magazine. The .40 S&W has an overwhelming share of the U.S. law enforcement market as a result.
Despite the .40 S&W's great popularity amongst American law enforcement and the private sector, it has yet to be adopted by a significant number of military forces worldwide. The mainstay for military use in the western world largely remains the preserve of the 9 mm Parabellum, or for a few special forces, .45 ACP in their respective adopted handguns. The United States Coast Guard, however, has adopted the Sig SauerP229R DAK in .40 S&W as their standard sidearm.
There are two major reasons for western militaries' choice of ammunition. The first reason is quite simply that the .40 S&W is not a NATO cartridge, and standardization is very important for logistical purposes.
The second major reason for .40 S&W not being chosen by military forces is the expense of procurement, purchasing and stocking spare parts, training of weapons techs to service and repair firearms, etc. The handgun is primarily a secondary firearm in the military forces of any country, and the expense can not be justified by whatever improvement is available over 9 mm equipment currently in stock for a secondary firearm. Special units, of course, are often free to use whatever they feel best suits their purposes and have designated funding to deal with that.
Since American law enforcement agencies are not bound by these constraints, most have chosen the .40 S&W round for its excellent ammunition capacities, accuracy, and superior ballistic performance.
Case failure reports
The .40 S&W has been noted in a number of cartridge case failures, particularly in Glock pistols due to the relatively large area of unsupported case head in those barrels, given its high working pressure. The feed ramp on the Glock .40 S&W pistols are larger than normal, which leaves the rear bottom of the case unsupported, and it is in this unsupported area that the cases fail. Most, but not all, of the failures have occurred with reloaded or remanufactured ammunition. Cartridges loaded at or above the SAAMI pressure, or slightly oversized cases which fire slightly out of battery are often considered to be the cause of these failures. These failures are referred to by many as "kaBooms" or "kB!" for short. While these case failures do not often injure the person holding the pistol, the venting of high pressure gas tends to eject the magazine out of the magazine well in a spectacular fashion, and usually destroys the pistol. In some cases, the barrel will also fail, blowing the top of the chamber off.
While the .40 S&W is far from the only cartridge to suffer from case failures, it is more susceptible for a number of reasons. The .40 S&W works at fairly high pressures (33,000 psi/230 MPa typical, but 35,000 psi/240 MPa SAAMI max) for a large caliber handgun cartridge, significantly more than, say, the .45 ACP. Since the .40 S&W is a wide cartridge for its length, and is often adapted to frames designed for the equally long but narrower 9x19mm cartridge, the length of the feed ramp must be longer to provide the same angle, which causes the feed ramp to extend into the chamber. This in turn leaves more of the case head unsupported. While this is not necessarily unsafe, it does reduce the margin of safety; when exacerbated by out of battery firing (leaving even more case head exposed) and potentially weakened brass (due to reloading) these factors appear to lead to the higher incidents of chamber failure.