The Return Of The 10mm Auto

Lazarus Rides Again
; .

10mm portability — Commander-style Springfield Ronin 9mm (top)
and Government-length Ronin 10mm.

10mm revolvers are still “A Thing,” including this Ruger GP-100.
Photo: Courtesy Sturm, Ruger & Co.

Smith & Wesson’s recent introduction of their Military & Police pistol in 10mm Auto is but the latest proof this caliber is undergoing a reasonably strong regeneration today. To understand why, let’s go back to the genesis of this Lazarus round.


Mas’ favorite 10mm: Mark Morris Custom Carry-Comp Colt Delta Elite,
shown with Norma’s original super-hot Ten loadings.

With 15+1 rounds of 10mm, the GLOCK 20 has almost become
the official “Alaska Bear Protection Pistol.”

A Brief History

In 1983, years of experimentation by Whit Collins and Col. Jeff Cooper had created the wildcat .40 G&A cartridge. The project came to fruition with the introduction of the Bren Ten and its new 10mm Auto cartridge, first produced by Norma. Produced by Dornaus & Dixon (D&D), the Bren Ten was a scaled-up version of a European 9mm pistol which had gained the colonel’s favor in almost every respect save caliber — the CZ 75, a selective-system double-action pistol that could also be carried cocked and locked. The Bren Ten even bore the raven logo of Col. Cooper’s school, Gunsite.

It had the load Cooper specified — a .40-caliber jacketed truncated cone bullet with an overall cartridge length much like the colonel’s beloved .45 ACP, stoked to a ferocious 1,200 feet per second. Chamber pressure was approximately 38,000 pounds per square inch. The colonel proudly noted the 10mm had as much energy at 100 yards as the .45 ACP did right out of the muzzle.

D&D, perhaps undercapitalized, did not last long. Guns were shipped without magazines when the subcontractor didn’t come through with them on schedule. The company was taking orders with full price to be paid in advance and many shooters were smart enough not to fall for it. When Dornaus & Dixon went out of business, it looked as if the 10mm Auto was “out of business” too.

Colt came to the rescue, chambering their Government Model for the new cartridge under the sobriquet “Delta Elite” in 1987. The Bren Ten had lasted long enough for it to be the signature gun of the star of the then-popular TV show Miami Vice. This put the gun somewhat on the public’s radar, though not so much as the movie Dirty Harry had done for the S&W .44 Magnum some 15 years earlier.

Something else had happened in the world of armed conflict that convinced some the 10mm’s time had come. For decades, cops had complained about being outgunned by criminals who had more powerful, higher-capacity guns than theirs. On April 11,1986, a hellacious gunfight in Miami, Fla., saw two vicious punks murder two FBI agents, permanently injure three and wound two more. The Bureau decided it might be time to switch from the six-shooter to the semi-automatic. Within the agency there were two almost equal factions — one wanted a pistol with 16 or so 9mm bullets and the other wanted .45s. John Hall, the brilliant head of the Firearms Training Unit at Quantico, split the difference. Tests with different loads convinced him a 10mm with a 180-grain jacketed hollowpoint at around a 1,000 fps, and 9+1 cartridge capacity would cut the Gordian knot, satisfy both sides and allow all the agents to confidently move forward into training for good hits in tactical circumstances. The FBI’s adoption of the 10mm in the Smith & Wesson Model 1076, built to their specifications, triggered a brief wave of 10mm popularity in law enforcement and naturally, armed citizen popularity for the Ten.


10mm versatility: You can get specially tailored “ruin-a-bruin” loads for the Ten …
… or “street-defense” tailored loads like Hornady’s Critical Duty.

Pistol is Springfield Ronin 10mm.

Change In Preference

The Bureau’s adoption in 1988 was well on the way to completion by 1990. However, this was the year S&W and Winchester introduced the .40 S&W cartridge. Conceived well before then as the wildcat centimeter round by Paul Liebenberg, the .40’s godfathers also included Tom Campbell and Whit Collins. It sounded the death knell of the 10mm’s popularity as a police/self-defense handgun.

Why? Remember the 10mm was the same OAL as the .45 ACP, necessitating a large frame. The shorter .40 could fit in any 9mm platform. It allowed more cartridge capacity and a smaller, lighter package and its standard load almost exactly duplicated the ballistics of the relatively mild “FBI load” for the 10mm. Soon, the .40 S&W was sending the 10mm service pistol to the police museum. Armed citizens followed suit.


The 16-shot 10mm is now popular as an outdoorsman’s pistol. This is Mas’ 10mm
Springfield Armory XD(m) 5.25". He appreciates the adjustable sights.

Another example of range of 10mm loads, Springfield Ronin 1911 shown.


The 10mm waxed and waned quickly in the police sector. The same was true in IPSC competition. The legendary Ray Chapman was still competing then and had Ed Brown make a custom Colt Delta for him. However, the slight ammo capacity advantage over the .45 in Major/Minor scoring was insignificant compared to the .40 after it came out. Chapman eventually returned to his signature 1911 .45 Auto and so did Jeff Cooper.

But there were other markets where the 10mm drew more interest. One was handgun hunting. The Magnum revolver and single shots like the Thompson/Center Contender ruled there, but people who preferred auto pistols saw the 10mm’s potential. In the late 1980s, I almost took my new Colt Delta Elite, fitted with a Mag-na-ported 6″ barrel by Larry Kelly at Mag-na-port, on African safari. I ended up with a .44 Magnum though, mainly because I feared I wouldn’t be able to replenish 10mm Auto ammo in the Republic of South Africa.

Hog hunters found the 10mm worked great on porkers. Chuck Taylor and others shot deer with it and were satisfied with its effectiveness. The full-power 10mm ammo of the originator, Norma, tended to over-penetrate on human targets, but the deep penetration made it all the more suitable for quadrupeds.


10mm accuracy: Mas finds the aptly named Dan Wesson Bruin
longslide Ten shoots nicely at handgun hunting ranges.

10mm shootability — 6'3" Marty Hayes (left) used a full-power 10mm to equal
5'10" Mas’ 300/300 score with 1911 and .45 hardball in double-speed class demo qualification.

The 10mm is popular at The Pin Shoot, and this one has brought
Sam Young to the prize table many times.

Bear Facts

This brings us to bears, and bear country was where the rebirth of the 10mm seems to have been engendered. The locus was Alaska.
Hunting is certainly popular on our nation’s Last Frontier. But so is hiking, perhaps more so, and not bound by season. So is fishing — residents of Alaska can harvest a virtually unlimited catch of salmon when the fish are running and they go to the streams in force.
And so do the bears.

During such times, a whole lot of Alaskans carry guns with them. Guns powerful enough to kill bears. Alaska has black bears and brown bears, including grizzlies and Kodiaks and even polar bears. The full-grown Kodiak has been known to reach 1,000 kilograms, or 2,204.62 lbs. A polar bear might be over 5′ high on all fours, and come close to 10′ tall when it rises on its hind legs. When someone in their environs feels a need to be armed but finds it unwieldy to carry a high-powered rifle or slug-loaded shotgun, a powerful handgun holstered on one’s person seems eminently logical.

For many years, supercop and martial arts/gun guru Jeff Hall, late of the Alaska State Troopers, noted the Ruger Super Blackhawk was practically the official outdoor handgun of the state. It was the lowest-priced high-quality .44 Magnum revolver. In recent years, the balance has tipped. I get to Alaska every now and then and the last time I was in Anchorage visiting most of their gun shops, I was told the title of best-selling gun there went to a couple of GLOCKs in a dead tie: the G19 9mm for carry in town and the G20 in 10mm for outdoor forays. Nowhere else have I seen such a wide array of 10mm Auto ammo on gun shop shelves.

Denmark’s Slaedepatruljen Sirius, a special operations/counterterrorist force, works largely in frozen wastelands populated by polar bears. After the 9mm rounds in their SIG P210 pistols failed to put down the huge bruins, they were issued 10mm GLOCK 20 pistols as standard.

Why did the less powerful gun replace the .44 Magnum six-shooter? Because, in a GLOCK 20, Springfield XDM or most recently a Smith & Wesson M&P, a polymer frame 10mm gives you 16 chances to stop a charging bruin.

The task is not easy. The target is coming at you like a freight train. The grizzly and other brown bears can hit 35 miles per hour at top speed. When they are targeting you, the frontal shot presents a very thick, sloping skull that tends to deflect bullets. A lot of outdoorsmen don’t think six are going to be enough.

Hence, the rise of the 10mm in bear country.

Now, let’s go beyond the borders of Alaska. According to, “There is believed to be a breeding black bear population in 41 of the 50 states.” In the classic words of federal law enforcement officer and trainer extraordinaire John Hearne, “It’s not about the odds, it’s about the stakes.” A person in bear country who says, “A bear would never attack me” is: (a) naïve, (b) virtue-signaling, (c) bear chow or (d) all of the above? No wonder the 10mm pistol is rising in popularity.


10mm versatility: All these different-purpose loads work fine for Mas.


To ruin a bruin is not the only good reason to have a 10mm. The FBI 10mm load, the 180-grain JHP at around 1,000 fps, worked every bit as well “on the street” as the original .40 S&W load, which essentially duplicated those ballistics. Full-power 10mms delighted Kentucky State Police troopers with its “stopping power” for years. The famously effective 125-grain .357 Mag hollowpoint hit 1,450 fps; the 135-grain full-power Ten is exactly as fast. A 158-grain .357 Mag averages 1,240 fps and 539 ft-lbs of energy; a 155-grain 10mm JHP from Underwood is spec’d for 1,500 fps and 779 fpe.

While the 10mm can easily exceed .357 Mag, the commonly stated “10mm = .41 Magnum” is only true with a narrow comparison. It seems to come from the fact in Winchester’s Silvertip line, popular with cops who chose each caliber, the 10mm load (hot for the caliber) was almost ballistically identical to the .41 Mag Silvertip (not loaded to max power for the caliber). In the heaviest hunting loads, the .41 can certainly be more potent than the Ten — but it will also have only six torpedoes on board ready to launch, not 16.
This time around, it seems, the 10mm is here to stay.

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