Is the .40 Dead?

By Tom McHale
Posted in #Gear
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Is the .40 Dead?

December 13th, 2019

6 minute read

The .40 died before it was born. That’s a rotten way to start a fulfilling life, but there you have it.

Thanks to a shortsighted, bean-counting corporate management team way back in 1978, the .40 B&S, the predecessor to what we now know as the .40, was denied production resources. The wildcat cartridge development effort had been advanced during lunches and after hours as a labor of love and was ready for its debut, pending management buy-in. Even though the test cartridges and pistols showed promise, leadership ixnayed the idea and what we now know as the .40 lay commercially dormant until 1990.

A man armed with a Springfield XD-M at work
Choosing the right chambering for your defensive handgun can be a tough decision.

Once it was commercially launched, the cartridge took off and blasted into the stratosphere. Offering a bigger hole and heavier bullet than a 9mm, and more capacity than a .45 ACP, it seemed to provide the balance law enforcement agencies were looking for. More stopping power than the 9mm and more capacity than the venerable 1911. Great, right?

A comparison of the 9mm and .40 S&W cartridges
The 9mm (left) offers softer recoil, while the .40 (right) slings a larger slug.

And it was widely adopted by law enforcement agencies across the country, with the civilian market following close behind. Of course, as with any cartridge, some in the gun community frowned upon the .40 as a lame compromise. Of course, no one who criticized it would want to be shot with one…

Is Less, More?

Anyway, fast forward to the present, and it seems like everyone is running in the opposite direction. All manner of law enforcement agencies and other tactical Delta Ninja Seal Mutant Turtle types are gushing about the virtues of the 9mm. Lots of notable agencies are switching from .40 to 9mm: The FBI, the LAPD, the Secret Service, and according to sources, Girl Scout Troop 439. The proof is in the pudding, right?

Comparing bullet diameter sizes between 9mm and .40 caliber
From left to right: Barnes TAC-XPD +P 9mm 115 grain, Federal Premium HST 9mm 124 grain, Barnes TAC-XPD .40 S&W 140 grain, and Federal Premium HST .40 S&W 180 grain.

Why? Modern ammo design has given us bullets that penetrate and expand reliably, thereby doing their intended job with predictability. Defensive bullets have to penetrate to adequate depths to perform their incapacitation function. Ideally, they’ll also expand in the process, again for the purpose of stopping threats as quickly as possible. While there are infinity trillion variables at play, 9mm, .40, and .45 ACP premium cartridges all perform those functions reliably. Make sure you check out Yamil Sued’s article on .45 ammunition for compact 1911 pistols if that’s your go-to handgun.

Do .40 and .45 make bigger holes? Yes. Does actual data from decades of use show statistically significant differences in metrics like one-shot-stops and shots to incapacitate? No. In fact, all three calibers perform almost identically. Apparently, the real world doesn’t pay attention to tropes like “Because shooting twice is silly.”

Two 9mm cartridges and two .40 caliber cartridges
The size difference between the 9mm (two left cartridges) and the .40 is immediately obvious.

If real-world street performance is roughly equal between the 9mm and .40, then why the big switch? For starters, the 9mm with its smaller cartridge diameter allows one to stuff more ammo into a gun magazine of similar size. And then there’s the recoil and ease of shooting factor. With less pain and muzzle flip, many people can shoot more effectively with a 9mm than the more powerful .40.

But is the .40 really dead? Consider some real data to explore the topic. You know, science and math.

Unfired 9mm and .40 S&W bullets
Modern bullet design has given the smaller 9mm (batch at left) a real chance to compete with the larger .40.

Going Back to School

Let’s start with power. I prefer to consider two dimensions of “oomph” when looking at a cartridge: kinetic energy (foot-pounds) and momentum. Kinetic energy reflects destructive power. Think about a power drill as having lots of kinetic energy. Momentum describes the ability of one object to whack and move another. Think wrecking ball. The classic foot-pounds number is undoubtedly useful, but it does emphasize velocity in the math, so fast-moving bullets will appear more “powerful” than slower-moving ones because there’s less emphasis on bullet weight. Momentum calculations, communicated as pounds-feet per second, weigh bullet weight and velocity more equally.

Four top loads for self defense
Tom tried out both Barnes and Federal offerings for his 9mm vs. .40 testing.

Let’s take a look at two options for both 9mm and .40 cartridges: a “standard” load and a faster, light-for-caliber load. To keep things simple, we’ll consider the Barnes TAC-XPD all-copper loads, which are generally on the lighter side, and standard weight Federal HSTs.

Table comparing specifications of 9mm vs. .40 S&W

No big surprise here. As most would guess, the .40 delivers more energy to the target than the 9mm. Does that matter? Maybe. Maybe not.

Note that there are other all copper 9mm rounds on the market like the 9mm Norma MHP load that uses a solid, machined bullet. These are substantially different concepts and are not included here for ease of comparison.

What about recoil? Recoil energy is one way to partially quantify what you feel in the hand when you press the trigger, so we can look at that. What’s tougher to put into simple numerical comparisons is the velocity curve of recoil, or how quickly the impulse hits you. Think about the difference between a cap and ball revolver and a modern pistol. The former is more of a slow push, while the latter has a snappy sensation.

Springfield Armory XD-M pistol, side view
The Springfield Armory XD-M 4.5″ pistol is offered in both .40 (shown) and 9mm.

Here’s how the recoil energy numbers shake out for the same cartridges. Since gun weight is an input factor, we’ll assume that we’re shooting a Springfield Armory XD-M full-size pistol. The 9mm weighs 29 ounces empty while the .40 tips the scales at 30.

Table of 9mm and .40 bullet velocity and momentum

Where It Counts

And herein lies the big reason that so many people are switching to 9mm. Recoil. For the “standard” 124- and 180-gr. loads of 9mm and .40, you’ll pay a 50 percent recoil energy tax if you choose the four bore — assuming you’re shooting guns of similar weight. Is that a bad thing? Not at all. If it’s your gun, and you train with it to the point of being able to tame that beast, knock yourself out!

After all, the reason that agencies switch from .40 to 9mm isn’t because no one can handle the recoil, it’s because more people can manage 9mm more easily. And it’s not like you don’t get anything in return. That investment in recoil buys you about a 12 percent increase in kinetic energy and a 27 percent increase in momentum, again for the standard weight bullets.

Hornady XTP bullets
So which one is right for you? Both the 9mm (left) and .40 are capable rounds, so it comes down to your personal preferences/needs.

So, what’s right for you? What is the best caliber for self defense? Choose the caliber that makes you feel all gooey inside. As long as you can control it, there’s nothing wrong with going with a bigger bore. Just don’t default to larger cartridges because someone says you have to. The 9mm does similar, but not identical, things with less recoil. But I still like it. Pick which one you like. Hate on the other. Or, just own both!

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Springfield Armory® recommends you seek qualified and competent training from a certified instructor prior to handling any firearm and be sure to read your owner’s manual. These articles and videos are considered to be suggestions and not recommendations from Springfield Armory. The views and opinions expressed on this website are those of the authors and do not necessarily reflect the views and opinions of Springfield Armory.

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Tom McHale

Tom McHale

Tom is a perpetual student of all things gun and shooting related. He's particularly passionate about self and home defense and the rights of all to protect themselves and their loved ones. As part of his ongoing learning, Tom has completed dozens of training programs and is a certified National Rifle Association instructor for pistol and shotgun. Tom is a professional writer by trade these days and has published seven books on guns, shooting, reloading, concealed carry, and holsters. In between book projects, Tom has published somewhere in the neighborhood of 1,700 articles for about a dozen gun and shooting publications. If he's not writing, you can probably find him on the range.

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