The .38 Smith & Wesson Special (commonly .38 Special, .38 Spl, , or .38 Spc, pronounced "Thirty-eight Special") is a rimmed, centerfire cartridge designed by Smith & Wesson. It is most commonly used in revolvers, although some semi-automatic pistols and carbines also use this round. The .38 Special was the standard service cartridge of most police departments in the United States from the 1920s to the early 1990s. In other parts of the world, particularly Europe, it is known by its metric designation 9x29mmR.
Despite its name, its caliber is actually .357–.358 inches (9.0678 mm), with the ".38" referring to the approximate diameter of the loaded brass case. This came about because the original .38-caliber cartridge, the .38 Short Colt, was designed for use in converted .36-caliber cap-and-ball (muzzleloading) Navy revolvers, which had cylindrical firing chambers of approximately .374 inch diameter, requiring "heel-based" bullets, the exposed portion of which was the same diameter as the cartridge case (see the section on the .38 Long Colt).
Except for its length, the .38 Special case is identical to that of the .38 Long Colt, and to the .357 Magnum which was developed from the earlier cartridge in 1935. This allows the .38 Special round to be used in revolvers chambered for the .357 Magnum (but not the reverse, the longer length prevents potential accidents from the significantly higher pressure generated by the .357 Magnum cartridge).
The .38 Special was introduced in 1899 as an improvement over the .38 Long Colt which, as a military service cartridge, was found to have inadequate stopping power against the wooden shields of charging Moros during the Philippine-American War. Most handloading manuals and other references date the cartridge to 1902 and the Smith & Wesson Military and Police revolver variation of that year.
Due to its blackpowder heritage, the .38 Special is a low pressure cartridge, one of the lowest in common use today at 17,000 PSI. By modern standards, the .38 Special fires a medium sized bullet at rather low speeds. The closest comparisons are the .380 ACP, which fires much lighter bullets slightly faster than most .38 Special loads; the 9x19mm Parabellum, which fires a somewhat lighter bullet significantly faster; and the .38 Colt Super, which fires a comparable bullet significantly faster. All three of these are usually found in semi-automatic pistols.The higher-pressure .38 +P loads at 20,000 PSI offer about 20% more muzzle energy than standard-pressure loads and places between .380 ACP and 9 mm Parabellum.
Only a minority of US police departments now issue or authorize use of the .38 Special revolver as a standard duty weapon, most having switched to the higher-capacity and faster-reloading semi-automatic pistols in 9mm Parabellum, .357 SIG, .40 S&W, or .45 ACP. It is still common in security use by guards who value the reliability and simplicity of a revolver, and by private citizens for concealed carry and police for secondary/backup handguns because its recoil when fired from very small and lightweight revolvers is considered much more manageable than more powerful cartridges; its low recoil is easier to control and is better acclimated.