The Versatile 10mm

First developed to combine the attributes of the 9mm Luger and the .45 ACP, this round is now one of the best handgun hunting cartridges made for semiautomatics.

Story and Photos by Jason Brooks

Handgun shooters know that two of the most popular calibers are the 9mm Luger (Parabellum) and the .45 ACP. The latter is slow but makes a big hole, while the faster 9mm tends to lose energy quickly once it hits the target but shoots fast and flat. In a perfect world, a gunmaker would bridge these two rounds to make a fast and hard-hitting bullet.
It is this very idea that led Lieutenant Colonel John “Jeff” Cooper to come up with what we now know as the 10mm Auto. Back in 1983, the search began by looking at the speed of the 9mm Luger and the energy of the .45 ACP. The idea was that if a round could shoot fast, which means flatter trajectory, and could hit hard, then it would fit the military’s need, as well as that of law enforcement and civilian use for self-defense. The 10mm was created by taking a .30 Remington rifle case and cutting it down to .992 inch and opening the mouth large enough to seat the 10mm (.400-inch) bullet.
Overall length is 1.240 inches up to an acceptable 1.260 inches. The round shoots 180-grain bullets very well, but loads are available for lighter and faster projectiles down to 135 grains, which shoot nearly 400 feet per second faster than the 115-grain bullet out of a 9mm. It is also loaded with 200-grain powerhouses that shoot around 300 fps faster than the 230-grain .45 ACP. It seems that Lt. Col. Cooper was onto something when the 10mm was developed.

FIRST CALLED THE 10mm Super, the cartridge never really shined. This could be because there was already a 10mm Super on the market so a name change had to be made; this set back the rise to fame, as shooters didn’t know what the 10mm was all about. In 1989, the FBI decided to issue the 10mm to their agents. This occurred after the shootout in Miami, Florida, in which five FBI agents were injured and two were killed when they attempted to arrest two bank robbers. The agents were armed with .357 Magnums and .38 Specials, both revolvers. After the incident the FBI realized they needed more firepower in their issued sidearms, both in ammo capacity and in bullet performance. Through testing, and like Lt. Col. Cooper, they decided the 10mm fit their needs. But there was one reason why the military and even the civilian world never really accepted the 10mm and that was felt recoil A fast and heavy round means there will be a bit of push back when you pull the trigger.
Smaller-framed agents couldn’t handle the recoil of the 10mm. When it comes to law enforcement, it is more important to hit your target with a light-shooting bullet than miss with a heavy one. For personal defense, a lot of times just producing a handgun will stop the encounter and then the loud bang could thwart the criminal. But for law enforcement, where each round has to be accounted for, it is imperative that the intended target is hit. Because of this, the FBI decided to go with another new round on the market, very similar to the 10mm, the .40 Smith & Wesson (S&W). The .40 S&W was built on the 10mm case and bullet, using the same 10mm projectile but in a shorter case that held less powder, shot slower and therefore had less recoil. Most law enforcement departments today use the .40 S&W.

Once again the 10mm loses its popularity before it really begins, but it doesn’t disappear completely. The 10mm Auto is a straight-walled cartridge that lends itself well to semiauto handguns. With faster velocities and harder-hitting bullets than the two most popular handgun rounds for self-defense, it took hunting guides and backcountry users to help this round shine. Some outdoor enthusiasts, including hunters, guides and hikers who ventured into grizzly bear country, would carry the light and fast .357 Magnum. Others would choose “hand cannons” such as the .500 Smith & Wesson, but most chose the .44 Magnum. All of these come in revolvers, which means limited ammo and slower followup shots, especially in single-action configurations while using one hand. Then gun manufacturers such as Kimber Arms, which teamed up with the Rocky Mountain Elk Foundation, started making the 10mm in the infamous 1911 model.

A TRIED-AND-TRUE DESIGN, the 1911 has been relied upon by the U.S. military in every war since World War I, until our armed forces switched to the faster 9mm Luger from the slow .45 ACP. So when it came time for Kimber and RMEF to come up with a handgun that would protect you in grizzly country, as well as function under stress with a time- and battle-tested platform, it only made sense they used the 1911. When it came to cartridges, it is no surprise that they chose the 10mm Auto. It has less recoil than the .44 Magnum, though it has near energy performance and hits harder than the .357 Magnum. Kimber came up with the 1911 Camp Guard, which sports a brushed silver frame, eight-round magazine and wood grips that are engraved with the RMEF logo and does the ever-overshadowed 10mm justice for the backcountry.
The Glock model 20 holds 15 rounds, nearly double that of the Kimber, and is often the choice of hunting guides. It is easy to use, nearly failsafe in harsh conditions and holds a lot of ammo. For the hunter, this extra ammo capacity is a bit much and adds weight to the handgun that is not needed. Of course you could not put all 15 rounds in the magazine but that goes against all training and recommendations, since the Glock model 20’s key selling point is that it does hold all that ammo.

For those who venture into bear country, they know the dangers are real. In the last 20 years there have been 60 fatal bruin attacks with 30 of those coming from grizzlies and a surprising 28 from black bears. Two were from polar bears and if you are attacked by a polar bear, then you have other concerns besides which handgun you are carrying, such as frostbite in July.
The 10mm hits hard enough to sting a grizzly and make it run away. A fatal shot would likely be at extremely close range and not necessarily instant unless hit in the head at the right angle. But stopping the attack is the end goal, not necessarily killing the grizzly on sight. But for black bears and other big game, the 10mm would do the job just fine, again at close ranges.

THE 10MM IS truly a semiautomatic handgun for the hunter. Those who choose to pursue deer, hogs, antelope, javelina, black bears and mountain lions with a handgun can carry the 10mm with confidence. For years the .357 Magnum was a popular choice and it always will be, but the 10mm ammunition manufacturers are marketing bullets for the hunter as well.
Hornady came out with a line of ammo last year known as Handgun Hunter. The bullet used in this line of ammunition is designed to hit hard and then expand faster than a traditional hollowpoint bullet. This is achieved by using a copper alloy that has a 95-percent weight retention and then the open cavity is filled with an elastomer material. When the bullet makes impact, the elastomer compresses, which pushes outward and causes the bullet to expand faster.

Thanks to this technology in bullet designs like this, a handgun is a viable tool for hunting. Other manufacturers such as Federal make lines of hunting-specific ammunition in the 10mm, including a 180-grain Trophy Bonded Bear Claw that leaves the muzzle at 1,275 fps. This round is perfect for deer-sized game, especially for hunters who use a tree stand where shots will be close and not rushed. For defending yourself in grizzly country, Federal also loads the 200-grain Swift A-Frame, which shoots 1,175 fps from the muzzle and at 100 yards is still traveling 1,020 fps. For a semiauto handgun, that is pretty fast and very hard-hitting with a 200-grain bullet.
The 10mm Auto is a good option for self-defense, either in the city or in the backcountry. It has been around for nearly 40 years, first developed to combine the attributes of the 9mm Luger and the .45 ACP, and is now one of the best handgun hunting cartridges made for semiautomatic firearms. When you need a lot of firepower and you need it now, the 10mm is one of the best options. Maybe it took so long to become popular because it is so versatile and each niche shooter couldn’t believe it would fit their needs, when in reality it fits them all.