The 10mm Auto is a semi-automatic pistol cartridge first developed by firearms expert Lieutenant Colonel John Dean "Jeff" Cooper and introduced in 1983. It was designed to be a medium-velocity pistol cartridge with better external ballistics (i.e., flatter trajectory, greater range) than the .45 ACP and capable of greater stopping power than the 9×19mm Parabellum. When FFV Norma AB (now Norma Precision AB) designed the cartridge at the behest of Dornaus & Dixon Enterprises, Inc. for their Bren Ten pistol (a newly developed handgun with design inspired by the CZ 75), the company decided to increase the power over Cooper's original concept. The resulting cartridge—which was introduced in 1983 and produced since—is very powerful, containing the flat trajectory and high energy of a magnum revolver cartridge into a relatively short, versatile rimless cartridge for a semi-automatic pistol.
The Federal Bureau of Investigation (FBI) briefly field-tested the 10mm Auto using a M1911 pistol. During testing of the caliber in 1988, it was decided that the full-power commercial load of the 10mm Auto was the best for law enforcement usage amongst all other semi-automatic pistol cartridges of the era, but it resulted in undesirable recoil for most agents.
Although it was selected for service by the Federal Bureau of Investigation in 1989 from the aftermath of the 1986 FBI Miami shootout, the cartridge was later decommissioned (except by the Hostage Rescue Team and Special Weapons and Tactics Teams) after their Firearms Training Unit eventually concluded that its recoil was excessive in terms of training for average agents' and police officers' competency of use and qualification, and that the pistols chambered for the cartridge were too large for some small-handed individuals. These issues led to the creation and following replacement to a shorter version of the 10mm that exists today as the .40 S&W. The 10mm outperforms the .40 S&W. This result is due to the 10mm Auto's higher SAAMI pressure rating of 37,500 psi (259 MPa), as opposed to 35,000 psi (240 MPa) for the .40 S&W, and the larger case capacity, which allows the use of heavier bullets and more smokeless powder.
The FBI Hostage Rescue Team, Special Weapons and Tactics Teams, and various other law enforcement agencies continue to issue or authorize the use of 10mm, including: the Coconut Creek Police Department, Plano Police Department, Weimar Police Department, and the San Francisco Bay Area Rapid Transit (BART) Police Department.
In military use, the government of Denmark has issued the 10mm auto to the Slædepatruljen Sirius (Sirius Sledge Patrol) headquartered in Daneborg, Northeast Greenland. The pistols were issued as a defense against polar bears which the unit encounters during patrols.The 10mm Auto is marketed for hunting, defensive, and tactical use and is one of the few semi-automatic, rimless cartridges that is legal for hunting in many U.S. states. The round makes the "Major" power factor ranking in the International Practical Shooting Confederation, even in lighter loadings.
Information gathered from the 10mm Auto Wikipedia page.