# 10mm Auto

The 10mm Auto (also known as the 10×25mm, official C.I.P. nomenclature: 10 mm Auto, official SAAMI nomenclature: 10mm Automatic) is a powerful and versatile semi-automatic pistol cartridge introduced in 1983. Its design was adopted and later produced by ammunition manufacturer FFV Norma AB of Åmotfors, Sweden.
Although it was selected for service by the Federal Bureau of Investigation (FBI) in 1989 in 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 too excessive for training average agents and police officers, and that the pistols chambered for the cartridge were too large to grip well for some small-handed individuals. These issues led to the creation of and following replacement by a shorter, less powerful version of the 10mm that exists today as the .40 S&W. While the 10mm hasn't attained the mainstream success of the .40 S&W, it has an enthusiastic group of supporters and users. There are currently more manufacturers offering firearms in this caliber than ever before.

## History

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 a design inspired by the CZ 75), the company decided to increase the power over Jeff Cooper's original concept. The resulting cartridge—which was introduced in 1983 and produced since—is very powerful, retaining the flat trajectory and high energy of a magnum revolver cartridge in a relatively short, versatile rimless cartridge for a semi-automatic pistol.
Quality control issues plagued early acceptance of the caliber, as a result of rushed production to meet numerous (some even defaulted) pre-orders of the pistol it was originally—as well as then being only—chambered for: the Bren Ten. An example is the peculiar circumstances surrounding the pistol's distribution at its primary release, leading to a number of initial Bren Tens sent to dealers and customers without magazines (the magazines themselves had complications). The relatively high price of the Bren Ten compared to other pistols of the time (manufacturer's suggested retail price was $500 in 1986, the equivalent of $1,200 United States dollars in 2021) was another factor in its demise, and the company was eventually forced to declare bankruptcy, ceasing operations in 1986 after only three years of inconsistent, substandard production. Had it not been for Colt making the unexpected decision in 1987 to bring out their Delta Elite pistol (a 10mm Auto version of the M1911) and later, the FBI's adoption of the caliber in 1989, the cartridge might have sunk into obsolescence, becoming an obscure footnote in firearms history.
Due to media exposure in the television series Miami Vice, where one of the lead protagonists had used the pistol as his primary signature weapon, demand for the Bren Ten increased after manufacturing ceased. In the succeeding five years, prices on the Standard Model rose to in excess of U.S. $1,400, and original magazines were selling for over U.S. $150.
The Federal Bureau of Investigation briefly field-tested the 10mm Auto using a M1911 pistol and a Thompson Model 1928 submachine gun as an "urban carbine" before adopting the Smith & Wesson Model 1076 in 1990; a short-barreled version of the Model 1026 with its slide-mounted decock/firing pin block safety supplanted by only a frame-mounted decocker. A contract was signed with Heckler & Koch to produce a quantity of the specialized MP5 utilizing the cartridge, designated MP5/10 for use by their Hostage Rescue Team and Special Weapons and Tactics Teams. Since 1994, both units still field the weapon and caliber to this day.
The 10mm cartridge was selected for Federal Bureau of Investigation use after a Wound Ballistics Seminar at the FBI Academy in September 1987, which managed to agree what a good cartridge would do, but couldn't agree if 9mm or .45 ACP could meet FBI requirements. In the same year, an informal test was conducted using a variety of available 9mm and .45 ACP handguns. The test indicated that only the type of 9mm round, described as "147 grain subsonic hollow point round produced by Winchester" had acceptable penetration. The test seemed inconsistent or contradictory to future observers, and it was accused of heavy .45 ACP and American handgun bias.
According to the latter 10mm report, it was decided: "five shots were fired in each of the 8 penetration tests, providing a total of 40 shots for each caliber or bullet type tested". The first selected was the 9mm described above. The second was a ".45 round, Remington 185 grain hollow point". The Wound Ballistic Workshop participants had a "consensus" that hollow points with "superior penetration" was what was needed.
The 10mm was picked as a "halfway" between the other two options, in terms of size. The "commercial loadings" had "high chamber pressures", which resulted in "heavy recoil" and "muzzle blast". A 180 grain hollow point bullet was "acquired and handloaded to a velocity of 950 feet per second". Later on, factory-loaded ammunition was acquired that met their requirements. During the trials, the 10mm was found to be comparable to the .45 ACP (Not surprising as the bullet weight and velocities were now so similar), but the 10mm was found to take up less space and produce shot groups on targets that were half the size.
As the FBI was adopting a 10mm cartridge closer in bullet weight and velocity to the .45 ACP, there was a need for large amounts of newly built ammunition of this type. This requirement was later submitted to Federal Premium Ammunition for production and further review. This became known as the "10mm Lite", or "10mm FBI" load, or attenuated 10mm, remaining common from various manufacturers today. With some pistol reliability problems increasing in this lighter load, Smith & Wesson observed that a version of the 10mm case reduced to 22 millimeters in length from the original 25 mm could be made with the retained performance parameters of the "10mm Lite". This altered cartridge was named the .40 Smith & Wesson. The shorter case allowed use in pistols designed with similar dimensions to those chambered in 9×19mm Parabellum, with the advantage that smaller-handed shooters could now have smaller-frame semi-automatic handguns. Colloquially called the "Forty Cal" and other synonyms, this innovation since became a common handgun cartridge among law enforcement agencies and civilians in the United States, while the parent 10mm Auto remains fairly popular and has shown a resurgence in recent years particularly among hunters.
Colt re-released their Colt Delta Elite series as generation 2 starting in 2009 where it ran until 2015. From 2016 to present, generation 2.5 has been in production. In 2015, SIG Sauer entered the 10mm marketplace with their P220 model chambered in 10mm. Ruger introduced a 10mm auto model to their popular SR1911 line in mid 2017, followed by their Blackhawk, Redhawk and 10mm GP100 Match Champion and Wiley Clapp models in 2018. The Springfield Armory XD-M series added a 10mm offering in late 2018. In November 2021, Smith & Wesson introduced 10mm Auto models in the M&P 2.0 series. In 2022 SIG released the 10mm Auto P320-XTEN in the P320 series. In 2024 Taurus released their first 10mm pistol, the 10mm Auto TH10 pistol in the hammer-fired TH line.

## Dimensions

The 10mm Auto has 1.56 milliliter (24.1 grain H $_2$O) cartridge case capacity.
10mm Auto maximum CIP cartridge dimensions
The common rifling twist rate for this cartridge is 406.40 mm (1 in 16 inches), 6 grooves, Ø lands = 9.91 mm (.390 in), Ø grooves = 10.17 mm (.4005 in), and land width = 3.05 mm (.120 in). A large or small pistol primer is used.
The CIP rulings indicate a maximum pressure of 230 MPa (33,000 psi). In CIP-regulated countries, every pistol/cartridge combination is required to be proofed at 130% of this maximum CIP pressure to certify for sale to consumers.
The SAAMI maximum pressure limit for the 10mm Auto is set at 37,500 psi (259 MPa).

## Performance

At mid-range potential, the 10mm Auto produces energy higher than an average mainstream .357 Magnum. The 10mm is slightly less powerful than the .357 Magnum with high-performing commercially-available ammunition, or hand-loaded .357 magnums, and well below standard .41 Magnum rounds. The cartridge is considered to be high-velocity, giving it a less arcing flight path upon firing (also termed "flat-shooting") relative to other handgun cartridges. More powerful loadings can basically equal the highest performing .357 Magnum loads, and retain more kinetic energy at 100 yards than the .45 ACP has at the muzzle.
The 10mm outperforms the .40 S&W by 150–300 ft/s (46–91 m/s) for similar bullet weights when using available full-power loads, as opposed to the "10mm FBI" level loads still found in some ammunition catalogs. 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.

## Usage

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 white-tailed deer in many U.S. states. The round makes the "Major" power factor ranking in the International Practical Shooting Confederation, even in lighter loadings.
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, Glasgow, Montana 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 Glock 20 to the Slædepatruljen Sirius (Sirius Sledge Patrol) headquartered in Daneborg, Northeast Greenland. The pistols were issued as a last resort defence against polar bears which the unit encounters during patrols.