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10mm Brass


History of the 10mm


The 10mm round was developed by Colonel Jeff Cooper for the 1911 style pistol and introduced in 1983. Col. Cooper thought that this platform was and is the best option for those serious about pistolcraft. While “Col. Cooper was a devout worshipper of the .45 ACP, he also expressed an interest in a pistol caliber capable of pushing a 200-grain bullet at 1,200 feet per second. And he thought that such a caliber would be ideal for times where we might require a pistol to reach out to 50 yards.” i The cartridge is more powerful than a 357 magnum and 41 magnum, and produces about double the muzzle energy as a 45ACP. Col. Cooper was deeply involved in the development of the Bren Ten, a pistol that was built around the cartridge, and was based off of the CZ 75.

After a shootout that occurred in April of 1986, two FBI Special Agents were killed by two bank robbers. The FBI had outnumbered the criminals, but were outgunned since their service weapons consisted of mostly 38 special revolvers and only a couple of semi-automatic 9mm pistols. This event became a one of the main reasons displaying that the 10mm had serious application in the law enforcement world and eventually became the FBI service round in 1987. However, after a short stint as the FBI’s service weapon, the cartridge was deemed as too powerful and had too much recoil for the average agent to effectively handle in a fire fight and it was removed from service.

An interesting side note is that during its employment by the FBI, the 10mm was loaded to slower velocities in an attempt to make shooting the round more manageable for the average agent. In a short period of time, many shooters realized that there was A LOT of unused case capacity in the 10mm, and shortened the case length to create the 40 S&W.

The cartridge saw a slight rise in popularity due to the fact that the character Sonny Crockett (Miami Vice, TV 1980’s) used a Bren Ten as his handgun of choice. It is also regarded as a great cartridge for hunting due to the heavier bullet weights and high velocities. In fact, it is one of the few semi-automatic rim-less cartridge that is legal for hunting white-tailed deer in the many U.S. states. There are still several law enforcement agencies and government agencies that use the 10 mm cartridge to this day.