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The 10mm: Thor’s Hammer for Semi-Auto Pistols

LJ Bonham is a semi-subsistence hunter, hunting magazine editor, and firearms enthusiast who lives in the Rocky Mountains.

The 10mm Auto is as close to perfect as any pistol cartridge can get.

The 10mm Auto is as close to perfect as any pistol cartridge can get.

It’s quite possible the 10mm Auto cartridge is the best, most versatile, pistol round ever developed. A bold statement given it almost disappeared from the market a few years back. Developed in the early 1980s, this wild child had several fathers, with combative pistol expert, John Dean “Jeff” Cooper, foremost. He thought the ideal self-defense round should drive a 200 grain, .40 caliber bullet at about 1000 fps. Cooper and his collaborators devised a cartridge based on a cut down .30 Remington case.

The 10mm debuted in 1983 housed in the ultra-exclusive, Bren Ten pistol. Norma, the famed Swedish ammunition concern, produced the fodder. The Bren Ten’s designers, however, changed the ammo specs from Cooper’s original. The round now boasted a 200 grain bullet at 1200 fps which produced muzzle energy equal to the .41 Remington Magnum revolver cartridge.

Despite high profile product placement on the TV show, Miami Vice, carried by hard-boiled, noir hero Sonny Crocket, played by actor Don Johnson, the Bren Ten failed in the marketplace. The gun fell off the charts. Its superb 10mm cartridge almost melted into obscurity until something terrible happened.

The ill-fated Bren Ten

The ill-fated Bren Ten

Disaster in Miami

In 1986, FBI agents attempted to arrest two sociopathic bank robbers in Miami, Florida. The heavily armed thugs shot it out for almost ten minutes with the G-Men. When the proverbial smoke cleared, two agents were dead along with the suspects. Five other agents suffered serious wounds, as well.

Despite bad tactics and multiple other problems, the Bureau rested the biggest blame on their standard issue pistol round: the 115 grain, 9mm Winchester Silvertip. In their opinion, the “Nine” didn’t have the power to penetrate deep enough on cross-body shots.

Never mind the one bullet they singled out did in fact kill one perp. It just took several minutes for him to bleed out in which time he killed two agents. Never mind almost any other contemporary auto-pistol round would have struggled under the same circumstances. Never mind the FBI already had a gun with the desired capabilities: their S&W .357 Magnum revolvers.

9mm S&W 5906, similar to the FBI's Model 459 used in the Miami shootout.

9mm S&W 5906, similar to the FBI's Model 459 used in the Miami shootout.

Monty FBI and the Holy Grail Cartridge

After the Miami debacle, the FBI decided they wanted a pistol round that would penetrate 12 – 18 inches into ballistic gelatin. Ammunition companies beat a path to Quantico, Virginia in hopes the Feds would pick their product. After exhaustive tests, one round stood out: the 10mm Auto from the ill-fated Ben Ten.

One problem: after the Bren Ten cratered, just one other 10mm pistol existed on the market. In 1987, Colt took a big risk. They offered their iconic M1911 pistol in 10mm. Dubbed the Delta Elite by Colt’s marketing mavens, it came either in blued carbon steel or stainless. It gained a small, but cultish, following. Yours truly owned one at the time and loved it.

The Bureau didn’t like the Delta Elite. Despite its venerable military pedigree, the gun’s single-action trigger mechanism gave them pause. They envisioned negligent discharge after negligent discharge by their agents. Never mind law enforcement officers in other agencies had used the 1911 for decades without significant problems. The Bureau suffered from classic NIH (Not Invented Here) Syndrome.

10mm Auto (left) vs. 9mm Parabellum

10mm Auto (left) vs. 9mm Parabellum

You Can’t Eat Your Cake and Have it Too

The FBI brass had their magic bullet, but instructors at the academy didn’t like the 10mm. Tests conducted during the search for the perfect round showed some smaller statured agents had problems with the stiff recoil.

After more research, the solution became clear: just water down the load a bit. Federal Cartridge produced what became known as the “FBI Load.” This launched a 180 grain, Hydra-Shok hollow point at 1030 fps. Almost what Jeff Cooper had envisioned a decade prior.

The Bureau’s Brick Gives Birth to a Compromise

The FBI put out a request for a 10mm pistol which met their perceived requirements. Again more tests, and in 1989, the Bureau adopted the Smith & Wesson 1076. Cherubim sang, and J. Edgar Hoover’s ghost smiled from on high.

In just a short time complaints from field agents flooded back to Quantico. They didn’t like the 1076: too big, too heavy. What’s a G-Man’s mother to do?

Back to the drawing board. Smith and Wesson, in collaboration with Winchester’s Western Cartridge division, created the .40 Smith & Wesson cartridge. It duplicated the 10mm FBI load’s ballistics in a 9mm Luger-length package. The Bureau dropped the 10mm and never looked back. Except for their Hostage Rescue Team (HRT)—they still use it when a perp has to be absolutely, positively stopped right now.

Simon (FBI) Says

People in law enforcement, and civilian gun owners, pay close attention to what gun and ammunition the FBI carry. When the Feds went with the 10mm, demand for the cartridge soared, and as soon as the Bureau dropped it, everyone ran toward the .40 S&W. Overnight the 10mm became a boutique cartridge and almost disappeared from the market for a second time. It held on by its proverbial fingernails, nurtured by handgun fans who wanted magnum-like power in a semi-auto pistol. Today, the 10mm is in a true renaissance. There are more guns available for the cartridge than ever before and ammunition is in good, if expensive, supply.

Head Over Heels in (10mm) Love

Given the 10mm’s up and down history, why should anyone bother with this red-headed stepchild? Power. Pure, simple, intoxicating power. The 10mm is the only cartridge for semi-auto pistols which fits into a normal-sized gun, produces magnum level energy, and is available in most gun shops.

The full-power 10mm duplicates the .41 Remington Magnum’s exterior ballistics in a semi-auto pistol. The .41 is perhaps the best all-around revolver cartridge in existence. The proven .41 hits hard enough to hunt medium game as well as defend against predators such as bears, yet most shooters can manage it one-handed.

We are, after all, talking about handguns, not hands-guns. The ability to engage targets rapid-fire with a one-hand hold on the weapon is imperative for self-defense shooting because one’s non-dominant hand is all too often occupied with a flashlight, baton, or grappling an assailant. The 10mm, despite the FBI’s protestations, shares these attributes with the .41 Magnum. The more powerful rounds out there, such as the .44 Magnum on up, are quite difficult to shoot one-handed.

(L-R): .45 ACP, 10mm, .40 S&W, 9x19mm

(L-R): .45 ACP, 10mm, .40 S&W, 9x19mm

Blinded by Science

.40 and .410 caliber bullets have high sectional densities compared to other handgun bullets. Sectional density is a non-dimensional decimal that correlates a bullet's weight and diameter. The heavier and narrower the bullet, the higher the SD, and the greater the tendency to penetrate deep into a target.

Here are the SD’s for the most common handgun bullets:

  • 9mm (.355”), 115 grain = .130
  • 9mm, 124 grain = .141
  • .38 caliber (.357”), 125 grain = .140
  • .38 caliber, 158 grain = .177
  • 10mm (.40”), 180 grain = .161
  • 10mm, 200 grain = .179
  • .41 caliber (.410”), 210 grain = .178
  • .44 caliber (.429”), 240 grain = .185
  • .45 caliber (.451”), 230 grain = .162

The FBI’s pistols in Miami were loaded with 115 grain bullets which have a low SD compared to the 158 grain ones used in their .357 Magnums at the time. Calibers with reputations for deep penetration such as .357 Magnum, 10mm, and .41 Magnum have SDs greater than .140.

There are other factors, as well. Velocity, bullet weight, and bullet construction have a big influence. Hollow-point bullets tend to penetrate far less than either fully jacketed round-nose or base-jacketed soft-points. When a hollow point opens up inside the target, its increased frontal area creates drag which slows it at a shorter distance. If construction is equal, though, a heavy bullet with a high SD will still go deeper, on average, than a light, low SD one. The heavy, high SD bullet also doesn’t need as much velocity to do its job.

Pure Energy

The last factor which determines how well a cartridge performs is the energy, expressed in foot-pounds, it generates. Effective hunting handgun cartridges generate 500 or more foot-pounds of energy at the muzzle. Cartridges with good reputations as fight stoppers generate about 350 – 450 ft-lbs.

The 10mm FBI load produces 440 ft-lbs from a five-inch barrel. Spot on for defense against human assailants. The 9mm Luger, .40 S&W, and .45 ACP also generate similar energy. .40 caliber cartridges, though, should penetrate deeper than others if bullet construction is the same.

For hunting, a full-power 10mm with a 200 grain bullet makes about 700 ft-lbs which is the same as a standard 210 grain .41 Magnum load. For comparison, a 158 grain .357 Magnum makes 530 - 550 ft-lbs, and an average 240 grain .44 Magnum around 750 - 800. The “Ten” is in good company. All this, plus a higher magazine capacity than a revolver and faster follow-up shots.

Get Real

What does this all mean, then? In short, if you want a handgun round to penetrate well, propel a narrow, heavy bullet at high velocity. The 10mm does just this when loaded to its full potential. A good thing if you intend to use it on game animals since you want a bullet that will drive deep into the vitals from unpredictable shot angles and smash through bone.

10mm bullets have balanced performance. They’re narrow enough to penetrate deep, yet wide enough to carve a useful wound channel, and heavy enough to resist deflection if they hit bone. They do this with less recoil than larger caliber cartridges. What’s not to like?

Bullet construction is the most important factor when choosing a 10mm load for a particular purpose. The cartridge’s beauty lies in the fact many loads can do double duty. Few, if any, semi-auto pistol rounds can make such a claim.

Full-power 10mm loads can serve for both hunting and self-defense which makes them ideal for someone who wants semi-auto firepower in bear country. If a person desires less recoil and intends to use their 10mm just for defense against human predators, the FBI load is still available from several ammo companies.

Some may claim the full-power loads are “overkill” for self-defense, but when someone is trying to kill you, there is no such thing. You just want to stop your assailant before they terminate your life, and a 10mm round will do just that—in a hurry.

10mm Winchester Silvertip (L) next to its infamous 9mm brother.  Decades after it's debut, the 10mm version is still a great, dual purpose load.

10mm Winchester Silvertip (L) next to its infamous 9mm brother. Decades after it's debut, the 10mm version is still a great, dual purpose load.

10mm Myths

There is much misinformation out there about the 10mm, propagated by the Mobius Loop called the internet. The "Ten" is a wonderful cartridge, but it is just a handgun round, not a death ray. Let's set the record straight.

  • The 10mm is not an armor-piercing round when loaded with conventional bullets. The video at the article's end will verify this fact.
  • A 10mm used for self-defense will create no more liability than any other handgun cartridge. A common prosecutor's tactic is to twist a defendant's intent in a jury's eyes by vilifying the gun or ammo the armed citizen used to save their life. If a defense attorney does not understand how to defeat this specious argument, get counsel who does.
  • The 10mm is powerful—for a semi-auto pistol cartridge. The newer big-bore, magnum revolver cartridges outperform the "Ten" by a wide margin, and even the least powerful center-fire rifle rounds are three or more times as powerful. Expect the 10mm to perform like a .41 Magnum, no more.
  • The 10mm is not "too powerful" for self-defense use. Yes, in its full-power guise it does kick, but any competent shooter who uses it in a full-size service pistol and puts in the necessary training time can master it. The same things were said about the .45 ACP for decades before the 10mm came along.
  • The 10mm is perfectly safe in Glock pistols if commercial ammo, made to SAAMI specifications, is used. Glocks are designed and tested to meet all industry standards and have an impeccable reputation in military, law enforcement, and civilian use. Glock specifically prohibits hand loads in their pistols.
Glock G20, 10mm pistol

Glock G20, 10mm pistol

These are the dual-purpose (hunting/self-defense) 10mm loads on the current market I’d recommend, but the list is not all-inclusive.

  • Federal 180 gr. Trophy Bonded flat point: 1275 fps, 650 ft-lbs. A great bear load, but might over-penetrate on humans so not the best for use in urban areas.
  • Winchester 175 gr. Silvertip: 1290 fps, 649 ft-lbs. Great deer and elk load. Might not have ideal penetration on bears due to designed-in rapid expansion. Great self-defense round.
  • Speer 200 gr. Gold Dot: 1100 fps, 537 ft-lbs. Same energy as a standard .357 Magnum, but with a much heavier and wider bullet. Good for deer, elk, and defense. While lower than preferred energy for bear, the Gold Dot bullet is exceptional and should get the job done if you place it right.
  • Hornady 180 gr. XTP: 1180 fps, 550 ft-lbs. (approx.). Another slightly reduced 10mm load in the .357 Magnum energy range, but the bullet performs well. Good compromise load for self-defense in bear country.
  • Underwood 200 gr. Speer Gold Dot: 1250 fps, 694 ft-lbs. The original 10mm ballistics are alive and well with this round. Another good dual-purpose load.

If bears are your main concern, there are several loads out there from companies such as Double Tap, Grizzly, and Buffalo Bore which feature 200 – 230 grain, hard-cast lead bullets. The makers state these are loaded to the maximum allowable pressure. I’d suggest before you try them, contact your particular pistol’s manufacturer and confirm these loads will not damage your gun. Some gun makers, such as Glock, prohibit using unjacketed lead bullets in their products. Another bear alternative is any full-power 180 or 200 grain full-metal jacket load. When it comes to bear defense, penetration is king, and expansion is a secondary consideration.

Platforms for the 10mm

These companies offer, or have offered, 10mm Handguns:

  • Colt
  • Glock
  • Kimber
  • Sig-Sauer
  • Tanfoglio
  • Smith & Wesson
  • Dan Wesson
  • Ruger
  • Rock Island

Hunting With the 10mm

So, what's it like to hunt with a 10mm? All handgun hunting is similar to bow hunting. You have to get in close, and you must expect to track a wounded animal after the shot. Handguns, even the 10mm, seldom put an animal down right away, unless you hit the central nervous system (brain or spinal cord). There are just a few semi-auto cartridges suited to medium game hunting: .357 Sig, .45 ACP +P, and 10mm. The "Ten" is the best in this class. To get more usable power in a handgun, you have to move up to a magnum revolver.

The Defense Rests, Your Honor

The 10mm Auto is as close to perfect as any pistol cartridge can get. It delivers magnum power, excellent penetration, and superb accuracy. When housed in a proper-sized service pistol such as the 1911, S&W 1006, or Glock 20, recoil is manageable. Ammunition is now available in almost any gun shop and there are more pistols chambered for it than ever before. A person who ventures forth armed with a “Ten” is well-armed, indeed.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2018 LJ Bonham


Rotterman on April 11, 2020:

Thank you for allowing me to join. I stumbled onto your site and was instantly hooked. Excellent writing and extremely informative.

Ed Palumbo from Tualatin, OR on May 03, 2018:

I enjoyed this article and video, The points were well developed. The tragic FBI shootout also demonstrated that the light 9mmP bullet was easily deflected by windshields. I look forward to the opportunity to fam-fire the 10mm and you've fueled that curiosity. Great job!

Readmikenow on May 03, 2018:

Very well done article. I liked the photos as well as videos. Enjoyed reading it.