10mm Auto

Lore & Background

The 10mm Auto was developed by FFV Norma AB for the Bren Ten pistol, a handgun inspired by the CZ 75. Early acceptance of the caliber was plagued by quality control issues due to rushed production to meet pre-orders, with some Bren Tens shipped without magazines. The high price of the Bren Ten—$500 in 1986—and the company's bankruptcy in 1986 threatened the cartridge's future. However, Colt's 1987 decision to produce the Delta Elite (a 10mm version of the M1911) and the FBI's adoption of the caliber in 1989 kept it from obsolescence. Media exposure on the television series Miami Vice, where a lead protagonist used the Bren Ten, drove demand after production ceased, with prices for standard models exceeding $1,400 and magazines selling for over $150.

The FBI selected the 10mm after a Wound Ballistics Seminar in September 1987 and subsequent tests. The cartridge was seen as a compromise between 9mm and .45 ACP. The FBI developed a reduced-power loading—often called '10mm Lite' or 'FBI load'—with a 180-grain hollow point bullet handloaded to 950 feet per second, before factory ammunition met their requirements. This loading was developed before any pistols were issued, contrary to claims it resulted from training complaints. The FBI adopted the Smith & Wesson Model 1076 in 1990, but problems with S&W 10mm pistols led to a recall in 1991. The FBI then issued SIG 9mm pistols as an interim solution. Smith & Wesson and Winchester subsequently developed the .40 S&W cartridge, which duplicated the FBI's reduced 10mm loading in a shorter case, allowing use in smaller-frame pistols. The FBI eventually adopted the .40 S&W in 1997 and used it until reverting to 9mm in 2015.

The 10mm Auto remains in use by the FBI's Hostage Rescue Team and Special Weapons and Tactics Teams, who have fielded the Heckler & Koch MP5/10 since 1994. The cartridge has shown a resurgence in recent years, particularly among hunters.

Reader's Guide

The 10mm Auto's significance lies in its role as a bridge between service pistol cartridges and magnum revolver rounds, offering high velocity and energy in a semi-automatic platform. Its adoption by the FBI after the 1986 Miami shootout marked a pivotal moment in law enforcement ammunition history, though the FBI's subsequent development of a reduced-power loading led directly to the creation of the .40 S&W cartridge. The .40 S&W, which duplicated the FBI's 10mm Lite performance in a shorter case, became a widespread law enforcement and civilian cartridge, while the parent 10mm Auto maintained a following. The cartridge's legacy includes its use by the FBI's elite units with the MP5/10 submachine gun and its continued popularity among hunters. The 10mm Auto's higher SAAMI pressure rating of 37,500 psi and larger case capacity allow it to outperform the .40 S&W by 150–300 ft/s for similar bullet weights when using full-power loads, though many commercial loads remain at the reduced FBI level. The cartridge's flat trajectory and retained energy at 100 yards exceeding the .45 ACP's muzzle energy contribute to its enduring appeal.