10mm Auto

The 10mm Auto (10&times;25mm, Official C.I.P. Nomenclature: 10mm Auto) is a semi-automatic pistol cartridge first developed by Jeff Cooper and introduced in 1983 with the Bren Ten pistol. Its design was subsequently improved then produced initially by ammunitions manufacturer FFV Norma AB of Åmotfors, Sweden.

Although it was selected by the Federal Bureau of Investigation in 1989 for field use from the aftermath of the 1986 F.B.I. Miami Shootout, the cartridge was phased out after their Firearms Training Unit eventually "concluded that its recoil was excessive in terms of training for average agent/police officer competency of use and qualification", and that the pistols that chambered it were too large for some small-handed individuals. These issues led to the creation and following adoption of a shorter version of the 10mm that exists today as the .40 Smith & Wesson. The 10mm never attained the mainstream success of this compact variant, but there is still an enthusiastic group of supporters who often refer to the .40 S&W as the ".40 Short & Weak".

History


The 10mm Auto cartridge was originally drafted and championed by eminent firearms expert Colonel Jeff Cooper. 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 Norma designed the cartridge at the behest of Dornaus & Dixon Enterprises for their Bren Ten pistol (a newly developed handgun borrowing base design from 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.

One of the first issues with early acceptance was the result of manufacturing problems with the Bren Ten. The contractor who was to manufacture the magazines were unable to deliver them on time and as such, many early Bren Tens were shipped to dealers and customers without magazines. The relatively high price of the Bren Ten compared to other pistols (manufacturer's suggested retail price in 1986 was U.S. $500) also contributed, and the company ceased operations in 1986 after only three years of inconsistent production. Had it not been for Colt's Manufacturing Company making the rather surprising decision in 1987 to bring out their Delta Elite pistol—a 10mm Auto version of the M1911 pistol—the cartridge might have sunk into obsolescence, becoming an obscure footnote in firearms history.



Thanks to media exposure (primarily in the television series Miami Vice), demand for the Bren Ten increased after production 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 F.B.I. briefly field-tested the 10mm Auto using a M1911-frame platform and a Thompson Model 1928 submachine gun before adopting the round in the late 1980s along with the Smith & Wesson Model 1076, a short barreled version of the Model 1026 with a frame-mounted decocker. During the testing of the new service caliber, it was concluded that the full power load of the cartridge would result in undesirable recoil. Subsequently, a requirement for reduced-recoil loading was then submitted. This later became known as the "10mm Lite", or "10mm F.B.I." load. Pistol reliability problems increased with this lighter load and Smith & Wesson saw this as an invitation to create something new: a version of the 10mm case reduced to 22 millimeters from the original 25. This altered cartridge was named the .40 Smith & Wesson. The shorter case length allowed function in a 9mm sized pistol; the advantage being that smaller handed shooters could now have smaller frame sidearms with near 10mm performance. Colloquially called the "Forty Cal", this innovation has since become a common handgun cartridge among law enforcement agencies and civilians in the U.S., while the popularity of the parent 10mm Auto still exists but has contrastingly diminished. Colt, Dan Wesson Firearms, Glock, Kimber Manufacturing, Nighthawk Custom, Smith & Wesson, STI International and Tanfoglio are some of the few manufacturers that still offer handguns in 10mm Auto.

The 10mm outperforms the .40 S&W by 200 - 250 ft/s for similar bullet weights when using available full power loads, as opposed to the "10mm F.B.I." level loads still found in some ammunition catalogs. This is due to the 10mm Auto's higher S.A.A.M.I. pressure rating of 37500 psi, as opposed to 35000 psi for the .40 S&W, and the larger case capacity, which allows the use of heavier bullets and more smokeless powder.

Cartridge dimensions
10mm Auto Maximum C.I.P. Cartridge Dimensions. All sizes in millimeters (mm).



The 10mm Auto has 1.56 milliliter (24 grain ) cartridge case capacity.

Common rifling twist rate for this cartridge is 381 mm (1 in 15 inches), 5 grooves, Ø lands = 9.91 mm, Ø grooves = 10.16 mm, and land width = 4.47 mm. A large pistol primer is used.

C.I.P. guidelines indicate a maximum pressure of 230 MPa. In C.I.P. regulated countries, every pistol/cartridge combination is required to be proofed at 130% of this maximum C.I.P. pressure to certify for sale to consumers.

The S.A.A.M.I. pressure limit for the 10mm Auto is set at 258.55 MPa.

Performance


At full potential, the 10mm Auto produces energy slightly higher than an average .357 Magnum load and below standard .41 Magnum rounds. The cartridge is considered to be high-velocity, giving it a less-curved flight path (also termed "flat-shooting") relative to other handgun cartridges. In its lighter loadings, the 10mm Auto is an exact duplicate of the .40 S&W cartridge. More powerful loadings can equal or exceed the performance of the .357 Magnum, and retain more kinetic energy at 100 yards than the .45 ACP has at the muzzle.

Some commercial loadings are as follows:
 * .357 Magnum: 676 ft.lbf for 180 gr at 1300 ft/s
 * 10mm Auto: 750 ft.lbf for 200 gr at 1300 ft/s
 * .41 Magnum: 938 ft.lbf for 250 gr at 1300 ft/s

The loads listed above are from a boutique manufacturer of high performance ammunition and are about maximum for S.A.A.M.I. established pressure levels in each cartridge. Free recoil energy of the full-power loads listed are 10.1, 12.1, and 22.9 ft·lbf (10.1 ft.lbf, 12.1 ft.lbf, and 22.9 ft.lbf) respectively for these cartridges, computed assuming a 40 ounce (2.5 lb, 1.15 kg) handgun.

Most major ammunition manufacturers offer 10mm loads closer in performance to the "F.B.I. Load" than the full-power 10mm; these still contain sufficient power for defense applications, but their recoil is more comparable to that of the .45 ACP in similar guns. However, some companies do continue to offer the original full-power ammunition.

Usage




The 10mm Auto is marketed for hunting, defensive, or 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. In regards to its use in personal defense, firearms author Chuck Hawks wrote:


 * "The most commonly available, reasonably portable, autoloader that might serve our purpose is the Glock Model G20, chambered for the 10mm Auto (.40 caliber) cartridge. The G-20 is as reliable as a powerful auto gets and relatively compact. This pistol comes with a 4.6" barrel, is 7.59" in overall length and weighs only 26.28 ounces. In recent years Glock has promoted the G20 as a hunting pistol. The EAA Witness DA autoloader is also offered in 10mm Auto and the Colt Delta Elite version of the 1911 Government Model used to be. There are probably others of which I am unaware."

Today, the cartridge is used as a high-power defense caliber against humans or animals, and for hunting by those who prefer the flatter carry profile and higher cartridge capacity of an automatic pistol versus a magnum revolver. It also makes "Major" power factor ranking in I.P.S.C., even in lighter loadings.

Despite the F.B.I. switching to the .40 S&W, there are still a number of law enforcement agencies that continue to issue the 10mm including the Albuquerque Police Department and the Anniston Police Department. In Canada, the Alberta Sheriffs also employ the cartridge in the Glock 20.

The government of Denmark has issued the Glock 20 to members of the Slædepatruljen Sirius (Sirius Sledge Patrol) in Greenland. The pistols were issued as a defense against polar bears which the unit encounters.

Synonyms

 * 10mm Bren Ten
 * 10mm Norma
 * 10mm F.B.I.
 * 10&times;25mm
 * The Centimeter (This name is also used to refer to a wildcat cartridge based on the 10mm Auto, which is trademarked by Pistol Dynamics.)