38 Special Ammo is a low pressure, medium sized cartridge that travels at somewhat low speeds. The fact that it's very accurate and produces little recoil makes it the most popular revolver cartridge in the world.

This ammunition 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 in 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.

And. because the 38 Special Ammo works in 357 revolvers, more shooters are opting for this ammunition due to the cost savings and reduced recoil. Good deals can be found, especially online, when buying in bulk.

The higher-pressure .38 +P loads offer about 20% more muzzle energy than standard-pressure loads and places them 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, .45 GAP or .45 ACP. It is still used commonly by private citizens for concealed carry and police as secondary/backup handguns because its recoil when fired from very small and lightweight revolvers is considered much more manageable than more powerful cartridges.