The 10mm Auto (10x25mm) is a cartridge for semi-automatic pistols, developed by firearms visionary Jeff Cooper and originally produced by ammunition manufacturer FFV Norma AB of Åmotfors, Sweden.
It was originally introduced in 1983 for the Bren Ten pistol, of Miami Vice fame. That pistol was later followed by the Colt Dela Elite and the Glock 20.
Adoption and Rejection by the FBI
In the late 1980s, the FBI adopted the 10mm round in the S&W 1076 pistol. This chambering was selected due to the Bureau's dissatisfaction with the performance of the .38 Special cartridge in the S&W revolver during the infamous 1986 Miami FBI shootout, in which special agents Gerald Dove and Benjamin Grogan were martyred by two criminals.
The FBI initially chose the 10mm Auto standard as being the most powerful then available for high-capacity semi-automatic handguns, with ammunition capable of exceeding 800 ft·lbf energy (doubling that of common 9mm rounds and handily exceeding the venerable .45 ACP). Shortly thereafter, the Bureau reversed its decision, switching instead to the .40 S&W cartridge, a round of the same 10mm diameter, but a shorter cartridge length (and less stopping power as a result of correspondingly reduced space for propellent in the cartridge).
The decision to change to the .40 S&W was caused by the inability of many FBI agents to cope with the recoil produced by a full-power combat cartridge. The length of the 10mm Auto cartridge necessitated a large frame handgun to accommodate the larger magazines and handle the stresses produced by the stronger round, meaning it was ill-suited to persons with small hands. At this point in the FBI's history, affirmative action programs had led to the hiring of a substantially different demographic than had been hired in the past. Further, many new recruits in the 1980s had generally been too young to have served in the Vietnam War, which combined with a general urbanization of the United States as well as politico-cultural pressures against legal firearms ownership, left the FBI with a pool of candidates unfamiliar with and uncomfortable with firearms. Accordingly, a change was made to a less-powerful cartridge that could be easily handled by the average recruit.
FBI statistics do not indicate how many shootings have failed to stop a suspect due to the usage of a reduced power cartridge.
Resurgence in popularity
The 10mm Auto languished in relative obscurity after FBI rejection as well as the paucity of civilian handgun offerings available (the Bren Ten having a troublesome history and with a production run of only 1,500). But interest was revived with the introduction of the Glock 20 in 1991, and increased considerable with the reintroduction of the Delta Elite (a 10mm variant of 1911 design) in 2009 and the Generation 4 Clock 29 in 2010. Coming with three 15-round magazines, the Glock 20 set the a high bar for other manufacturers.
The 10mm is considered to possess adequate stopping for all North American wild animal threats, including brown bear (although care should be taken in choosing ammunition for that purpose, as heavier hard-cast loads are recommended over hollow-point personal defense rounds). After-market barrel and spring replacements (for the Glock 20's stock polygonal barrel and spring) are offered by several third-party manufacturers for Glock customers seeking the fire heavier loads or reloads.
Those competing in tactical shooting competitions (IDPA, IPSC) sometimes use the S&W 610 10mm revolver, since the 10mm cartridges can be united by a single "moon-clip", giving the shooter a reloading speed advantage over the traditional revolver.