10mm auto vs .40 S&W: The Brother War | The Dead Calibers Archive

The Intwined development
of 10mm Auto & .40 S&W

We begin with origins – the 10mm Auto was introduced in 1983, and after the FBI’s notorious 1986 Miami shootout (which exposed the limits of ammo at the time), Smith & Wesson/Winchester developed the shorter .40 S&W round in 1990 to meet the FBI’s performance expectations. However, there’s much more to this story and we dive into some of the earliest 10mm/.40 Caliber pistol cartridge experiments and how we ended up with the 10mm Auto and the .40 S&W we know today.

Is 10mm the Best Millimeter?

The 10mm Auto is an interesting round, going from seeking to fill a gap in the market, to fading into obscurity, and now becoming a more popular, if still somewhat niche choice.

Yet the 10mm of today is not what it seems, nor what it was envisioned to be.

10mm is truly a strange beast, at once it seems to have those that swear by it, yet others who see it as a less practical stop gap, however to talk about it there are actually two other cartridges that we can’t leave out of our story, as their histories are almost just as intertwined with the 10mm Auto as its own.

Today on the Dead Caliber’s archive, we’ll talk about the 10mm, it’s various incarnations, and maybe give you some insight into why this round faded into the background and where it sits today, despite the modern hype around the round.

Normally, I’d start at the beginning of the story, but the 10mm probably would not have the same level of notoriety if not for its consideration in the wake of one of the most notorious kerfuffle’s that the FBI got into.

The Miami Shooting

While the topic has been discussed and dissected in much more detail than I dane to dictate at this demarcation the necessary dictum that you need to decern is thus.

Eight FBI agents armed with mostly revolvers, a semi-auto pistol, and a shotgun, faced a Mini-14 wielding misanthrope and his partner.

The agents ended up either wounded or worse, and law enforcement was forced to reevaluate their tactics, training, and ammunition selections.

While the lessons learned to be learned from this are arguable, Mr. Paul Harrell has a discussion that breaks down and summarizes the major lessons to be learned from the shooting for those that are interested.

For our purposes today, one of the lessons that was learned was the need for better ammunition selection as a single round of 9mm failed to sufficiently penetrate the Mini-14 wielding mad man and end the fight immediately. Beyond just better ammo, the FBI felt that they needed to move away from the six shot revolvers and to semi-auto pistols as well as a standard.

From the aftermath of the shoot out the FBI ballistics protocols were developed in 1987.

These protocols set out the standard that we use today,

12 to sixteen inches of penetration into ballistics gel after passing through various barriers, such as glass, car door analogs, heavy denim clothing, and drywall.

Of the various calibers that were tested, the main competitors were the 9mm and the .45 ACP.

However one caliber, would be almost snuck into the running. A new cartridge and the center piece of our story today.

THE .40 G&A and the 10MM AUTO

But how exactly did a recently developed round, with little history and at that time exactly two major production pistol models manage to find itself up for consideration by one of the major law enforcement agencies of the US federal government?

Well, to answer that question, we need to go back to 1972.

In 1972 firearms writer Whit Collins noted that there existed a gap between the “TWO WORLD WARS”
.45 ACP and the “It was meant to wound” 9mm Luger.

While I’m sure that Collins was not the first to think to himself that huh, what if there was something between 9mm and .45 ACP, he was the first to actually DO something about it.

With the help of John French, he developed the first version of a .40 caliber, 10mm semi-automatic pistol cartridge.

Using modified 30 Remington rifle cases, Collins and Frech were able to create a round that pushed a 180 grain bullet to 1110 feet per second, out of a 4.7 inch barrel, using a modified Browing Hi-Power as a test platform.

While this testing showed that the wonder nines of the era could be modified to fit a slightly larger round comfortably, the .40 G&A project failed to spark serious interest with any firearm or ammunition manufacturers, and the .40 G&A wildcat faded into the background for over a decade.

Basically the collective gun industry went “neat” and promptly went back to arguing over 9mil vs. .45 and how much more “reliable” revolvers are compared to semi-autos.

Fast-forward to 1983.

Jeff Cooper, who probably needs no introduction to many shooters, but for the uninitiated, was a key driver of the modern handgun shooting techniques, is consulting for Dornaus & Dixon on the pistol that would be known as the Bren Ten.

Essentially, Cooper, bringing in more shooting world star power than anyone else at the time would have guaranteed that people would be interested in the pistol simply because his name was attached to the project.

However, Dornaus & Dixon would do their best to screw up what should have been, on paper, an incredibly popular handgun. However, we’ll get to that in more detail later.

When selecting a cartridge for the pistol Cooper wanted more power than the .45 or the 9mm.

Having been familiar with the .40 G&A wildcat, Cooper liked the idea but, again, wanted more power out of the round.

The goal would be to push a 200 grain bullet at 1200 feet per second. Some may note that this is roughly similar to the goals of .45 Super or .460 Roland, but both of those rounds really should be topics for a later date.

Cooper, with his industry fame, would be able to get Norma to take this design seriously and Norma produced two factory loadings at first.

A 170 grain JHP @ 1400 FPS and a 200 grain FMJ @1200 fps.

However, it would soon become apparent that these loadings were too much, not just for shooters, but for the guns themselves. Cooper wanted power, and he may have gotten too much of a good thing with these early 10mm loadings as guns were battering themselves apart.

Norma would reduce their factory loadings. The 170 grain bullet would be slowed down to 1300 fps, and the 200 grain bullet would be brought down to 1120 fps.

Yet, Norma was not the only ones who noticed that the 10mm, as Jeff Cooper designed it, was a bit much for shooters and pistols.

The FBI, during their ballistics studies and testing rapidly moved to a lower power loading of the 10mm.

This loading would push a 180 grain bullet 950 feet per second and be informally known as the FBI 10mm “lite” loading developed by the FBI, specifically Special Agent John Hall the Firearms Training Unit Chief if I am to understand correctly.

Desiring a handgun for this round, the FBI would solicit manufacturers for a pistol to use this round. While others such as SIG-Sauer were courted, it would be Smith & Wesson that would eventually take up this challenge, despite the corporate issues that they were dealing with at the time.

Agents such as John Hall and the one who was responsible for including the 10mm in the testing, also were weary of trying to ask for funding to move from 9mm and .38 special revolvers to the .45 ACP, a round that the military had just moved away from.

Thus the 10mm gained another mark in its favor, beyond the good test results, a bureaucratic one, sure, but it was another reason to consider the 10mm for the FBI.

So 10mm had another mark in its favor, in addition to preforming well in the FBI testing, but it would be in a slightly different form than the original Norma loads. Again the FBI was favoring a “light” loading of the 10mm for use by their agents.

Now, Smith & Wesson was struggling to maintain their hold on the law enforcement market with the introduction of pistols such as the Glock 17 and other wonder nines. This was compounded by management issues and flagging quality control issues.

Despite these challenges, Smith & Wesson would introduce the Model 1076. A modified Smith & Wesson auto pistol that integrated a frame mounted de-cocker, possibly indicating that the FBI really wanted a SIG P200 series pistol, but settled for Smith & Wesson’s offering, unable to get SIG to produce a 10mm pistol, as they are rumored to have approached SIG about this and SIG declined.

In total 9500 pistols would be contracted for by the FBI from Smith & Wesson.

However, this FBI, “lite” load that was being used would spur a revival of the .40 G&A.

.40 G&A Comes Back

In the background of these events, the .40 G&A would have its development be revived.

Collins had taken back up work on the .40 G&A, and would refine it into a new cartridge, the 165 grain bullet running at 1075 feet per second would be christened as the Centimeter.

This round would see interest from Pachmayer but commercial production of pistols would not start, instead, the former Customers Shop manager at Pachmayr would leave and form his own gun smithing business.

This manager, Paul Liebenberg, would go on to produce 1911 conversions for the Centimeter and it gained a following in the IPSC due to the higher capacity but equal scoring to the .45 ACP.

Of these shooters Tom Cambell, an employee at Smith & Wesson would start to lobby for the .40 Caliber Centimeter to be adopted by Smith & Wesson as a round to be marketed to competition shooters.

Due, in part to Cambell’s lobbying, Smith & Wesson would refine the round into the .40 Smith & Wesson that we have today for a first reveal at the 1990 Vegas Shot Show.

The Centimeter, would, as it turns out, be able to match the 10mm loadings that the FBI was using in a smaller form factor. A perfect cartridge to pitch to the FBI and the general public.

It was ballistically what the FBI wanted, and the shooting public was already, technically familiar with it through its use in the IPSC.

Now, as legend has it. Our, at the time upstart pistol designer, Gaston Glock, would be in attendance.

Most in the industry knew him by reputation rather than on sight, so Heir Glock was able to sneak over to the Smith & Wesson booth and pocket a few of the cartridges that Smith & Wesson was producing for their soon to be released Model 4006 pistol.

Glock found that the 17 could be easily retrofitted with a .40 caliber barrel and a slightly stiffer spring, allowing him to release the Glock 22 just a week before the Smith & Wesson pistol would come to market for the round.

While the drama over police contracts, the .40 S&W cartridge between Smith & Wesson and Glock would continue to play out for years to come, the .40 S&W cartridge would prove to be the very thing that the FBI was truly looking for.

While the 10mm was a longer and larger case, the shorter .40 S&W would prove to be just as effective when loaded properly as the light 10mm loadings the FBI was using in their testing.

Between this, the smaller cartridge offering a smaller, easier to manager pistol, and finally ongoing issues with the 1076 pistols failing to function, the 10mm found itself sidelined by the very round that it helped to create, or spawned from, depending on how you want to look at it.

Of course, the .40 S&W would continue to be the default for the FBI and other law enforcement agencies for quite some time to come until the ultimate decision to move over to the 9mm.

The 10mm meanwhile would languish in relative obscurity, but would retain a strong, cult, following that endures to this day where the .40 S&W has seen it fall out of favor while the 10mm is becoming regarded as the more powerful round.

Many law enforcement agencies, especially those in Alaska or northern areas that need to deal with large animals, bear, moose, etc. on a regular basis, still use pistols that chamber the 10mm round because, when properly loaded it does remain an effective tool for dealing with these kinds of threats.

Major 10MM Pistols

hen it comes to 10mm pistols there are some major pistols that we can discuss.

Of course, no discussion of the 10mm AUTO should fail to leave out the Bren Ten pistol.

Not only the gun that helped to popularize the 10mm AUTO as a cartridge, it was influenced by the guidance of Jeff Cooper in its design.

The pistol was based primarily on the CZ-75 9mm pistol, scaled up to accept the 10mm cartridge that was developed alongside it.

The pistol had a number of unique features, it could be carried cocked and locked, along with a cross bolt safety on the slide. Almost uniquely it was able to be adjusted so that the magazines could either drop free or retained in the grip with a simple screw adjustment at the base of the grip.

Basically, this pistol was about as tactical as any high speed low drag operator could ever want.

Metal sights meant for racking on a belt or boot, DA/SA trigger, high capacity, high power cartridge, it was designed with just about everything in the then current cutting edge pistol tactics and training mind.

Another feature was that the Bren Ten’s original magazines were designed to hold either .45 ACP or 10mm AUTO. However, that is where the troubles start for this pistol.

This design idea turned out to be a poor one and the magazines failed to be reliable and the magazine OEM, Mec-Gar, had to redesign a dedicated 10mm magazine. This lead to many guns being shipped without magazines at all.

I’m not even an engineer and I struggle to think why they thought this would be a good idea. It just sounds like an easy way to make an unreliable magazine.

Beyond this Dornaus & Dixon utilized MIM parts, but failed to do proper quality control leading to further issues with reliability and durability, and pair that with a hot round like the 10mm that when loaded to Norma’s original specifications, would beat up on the gun, you get a recipe for problems.

This lead Dornaus & Dixon to eventually become trapped in a negative cash cycle. Guns would go out, but come right back in for repairs, eating into their profits and keeping the company permanently in the red.

Due to this the company soon shuttered in 1987 with about 1400 pistols in total produced.

There were, however, three versions produced, a standard model, a Cooper Commemorative model, and a Tactical model with a 4″ barrel. Today the pistol retains a bit of a cult collector following with examples becoming rather sought after because of the history and associations of the pistol. Both in the shooting world with Jeff Cooper and popular media with Miami Vice having featured the pistol prominently.

Colt Delta Elite

The next notable pistol was the Colt Delta Elite. This was the pistol that the FBI was using during its testing of the 10mm auto. Colt Seeing the potential in the 10mm cartridge essentially took their 1911 pattern pistols and scaled it up slightly for the 10mm auto. Releasing the Delta Elite just as the Bren Ten was falling out of the market.

Several versions of the Delta Elite were produced, with Gold Cup and Match Versions. However, there were some changes beyond just slight geometry adjustments. The Delta Elite would use a nested recoil spring design to help deal with slide velocity issues. A cut out would be made into the side of the frame to deal with stress fractures, again due to the more powerful 10mm loadings. This would become a more common change on 1911 pistols, even with pistols not chambering 10mm.

For the delta elite, models could be found either blue or in stainless, with a DE prefix on the serial number for the blued models and DES for the stainless steel models.

Beyond this the Delta Elite was essentially just another 1911, for better or worse.

Another major pistol in the 10m auto story is the Smith and Wesson Model 1076. The 1076 was much the same as many of Smith & Wesson’s third generation of auto loading pistols of that era, but as previously noted the slide mounted decocker would be removed in favor of a frame mounted one.

While the FBI would contract for 9500 pistols but the reliability issues and the eventual switch to .40 S&W saw only 2400 pistols actually be delivered.

The 1076 would live on in the civilian market, kind of, in the 1006, but the 1006 would retain the slide mounted decocker.

Both the 1076 and 1006 were full sized guns and featured DA/SA triggers. Like much of the Smith & Wesson Pistols of the era, they were “fine”.

I’ve owned a 9mm Smith and Wesson of this era, and it was nothing amazing, but I couldn’t overly fault it either. I started shooting revolvers, and have never been overly snobbish about long and heavy triggers, even though they are objectively worse than a short, crisp, single action trigger.

Finally we should briefly discuss the Glock 20. Probably the main stay of modern 10mm handguns.

Of course, it’s a Glock. Same size as the G21 in .45 ACP, just running the 10mm. If you know Glocks, you probably know the G20, it just kicks harder.

But where does the 10mm stand today?

Modern 10mm is a Hot .40 S&W

Here’s probably what I’ll get the most amount of hate for.

I need to break it to you that most of today’s 10mm is pretty much .40 S&W +P at best.

Comparing the 180 grain hydrashock out of a 5″ barrel in both calibers gives you 1069 fps for 10mm and 1051 fps for .40 S&W.

This kind of issue is not just apparent on the 180 grain hydrashock. Plenty of loadings have this exact same issue.

Now there are more, hotter loads, for 10mm than just this, but you should be aware that a lot of the 10mm loadings on the market are just above the .40 S&W at best and not to the same standards as the original Norma Loadings that the cartridge was first using.

Remember the metrics that I quoted earlier, Norma started with 170 grain loads at 1400 and then 170 grains at 1300. This is where the 10mm was originally supposed to be.

The two that I am aware of that truly give the 10mm the power it is supposed to have are the loadings from Buffalo Bore and Underwood. The rest are patterned after the “light” FBI loadings or somewhat hotter.

Basically if you are shooting a .40 S&W today, that’s pretty much the 10mm loading and ballistics that the FBI wanted from the original testing they did in 1987 at their ballistics lab.

Unless a 10mm loading exceeds this .40 S&W base line, it’s not a full power 10mm and you might as well run a .40 S&W and get the shorter grip diameter, if that’s more comfortable for your hands. Also you have the slightly disadvantage that a longer case brings when it comes to reliability.

With all cartridges, it’s a trade off, and you just don’t get a free lunch for anything. Tweak one thing here and all of the sudden you have a problem over there that you didn’t realize.

Perhaps that’s why the cartridges that we are using today are so bloody old. The 9mm Luger, is essentially a 124 year old design. Sure we’ve tinkered with the bullet and powder, but the dimensions are roughly the same. Much bigger and you start either sacrificing capacity, or you get a gun that’s more difficult to use effectively. Much smaller and you start losing even more effectiveness in a handgun format.

I see you 5.7 fan’s don’t come at me, I’m not knocking that either, I’m just trying to not get too far into the weeds. I’ll give the 5.7 and other rounds it’s due eventually.

So let’s get back on track.

Now that is not to say that the 10mm does not have a place in the modern American arsenal.

10mm Auto Use Cases

Tim Sundles, of Buffalo Bore has done a number of talks about the 10mm and other “magnum” power semi-auto calibers.

The long and short of it, if I may attempt to drive at what Mr. Sundles is getting at, and he’s welcome to correct me. Is that the 10mm is a good handgun hunting round because it carries a flatter trajectory, and more energy over distance.

However, Mr. Sundles prefers larger caliber rounds such as the .45+P or .45 Super for a “stopping” round. Ie one that is meant to immediately stop a charging animal.

I’ll defer you to his videos on the topic for a more in-depth discussion of those various calibers and how they compare to one another.

Tim Sundles has plenty of hunting experience, and started Buffalo Bore, so I have little reason to doubt his expertise, even if some of his data is antidotal.

As much as I love experiments with repeatable results, hard measurements, and studies, I can’t completely discount first hand, hard won experience in the ultimate synthesis of effective ballistics.

Plenty of projects of the SPIW era of military development showed us, as good as it looks on paper, that shine might not really translate to the real world where you have hundreds of other variables that you can’t account for easily.

But what about outside of hunting?

Well I could see an argument for a Pistol Caliber Carbine in 10mm.

Looking at Ballistics by the Inch’s historical data, the 10mm out of a 16″ barrel is withing spitting distance of the .223 when it comes to energy at the muzzle. Now of course, that comes with the cavate that you are probably sacrificing magazine and or ammo compatibility with your pistol. Or you are now carrying a 10mm pistol that is more challenging to use compared to a 9mm and more expensive to train with.

And you’re still running a pistol caliber, a good pistol caliber, but a pistol caliber none-the less.

Now in a pistol format, the 10mm is, like all handgun rounds, an inconstant at best “man stopper”.

Younger viewers might not be as engrained with this fud lore but when it comes to handguns there is no stopping power.

Tales and antidotes about such and such, WWII killed him with one shot, yada yada yada, it’s not real. What is real is hits to the central nervous system. Hit that and someone will stop, hit the heart and they have maybe a few minutes.

I have yet to see any data, beyond an individual self-defense situation, that suggests that a specific handgun caliber has any major advantage against a person over any other caliber. I am open to be wrong about this however, my current and best understanding is that no matter what you do to it, pistols suck, rifles get stuff done.

And honestly, it’s probably because of what is getting holes poked in it.

Let me explain.

10mm Auto for Self Defense

Humans are thin skinned, weird animals that can keep going at times when an animal with the same kind of damage would have given into shock. Conversely, humans can be “more” susceptible to a “psychological stop” in some ways. Going bat shit, freezing, or otherwise just locking up because an acorn hit a car door next to them.

But in all of this strangeness, no handgun has really been shown to be as effective as a rifle round screaming out of a much longer barrel with a larger powder charge.

Of course, when dealing with combat, self-defense, etc. the best gun is the one you have, and I’m not one of the men who’s called out to do dangerous things in dangerous places, with dangerous people. So take my opinion for what it’s worth, just another opinion, subject to all of the associated fallibility of human error and limited by the resources and training that I have access to.

So, at least to me, while I’m still fond of the 10mm, and its son, the .40 S&W, I understand that being able to train and more easily control recoil with the 9mm are factors that win out, at least for me when it comes to a handgun.

Your personal preferences, and particular persuasions, are of course permitted to persist with no pessimistic projections or pontifications from yours truly.

You do you. I’m not going to knock you for enjoying or carrying something that is not a 9mm. I would just encourage you to train with it.

Thus we come to the last bit that I want to point out as something worth discussing, if for no reason than it may be dangerous.

Occasionally it is said that the .40 S&W can be fired out of a 10mm chamber.

Please don’t.

First I will never encourage a shooter to use ammunition that is not intended for your firearm. An while there’s plenty of silly this not that in the world of 5.56, this is one situation where it is ill advised to risk yourself and your firearm by trying to shoot the much shorter cased .40 S&W out of a 10mm pistol.

You can see what the over pressure events look like when this is tried.

Some success has been noted with striker fired guns, but you’re doing something that’s rolling the dice.

The meme of, “if it seats it yeets”, is probably the most dangerous idea out there. Just please don’t risk it.

So with that Public Service Announcement out of the way, let’s wrap up the post.

10mm Auto Today

Honestly I am somewhat happy that 10mm is getting a bit of a second wind today. It’s a good case and I think a 10mm PPC could be an excellent option for getting a bit more oomph out of a carbine when loaded like it should be.

10mm is decent enough out of a good handgun to go hunting deer with, even larger game, and I’m certain that no one with ill intent would want to be on the wrong side of the muzzle of such a hand cannon.

However, you should be certain that your gun is set up for the real 10mm loadings if you are going to be shooting them on a regular basis.

The bottom line is this –

The 10mm is a good round, and while it does have weaknesses that should be pointed out, such as recoil, many “lite” loadings on the market, and a propensity to be a more expensive option. I would just encourage you to examine your use case for if you really need it or not.

it remains one worth considering if you are looking for more power from a pistol or pistol caliber carbine for use in the woods.