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When it comes to pistol debates, you’d be hard-pressed to find a topic that’s been batted around more than 9mm vs 40 S&W. What kicked the argument off was an infamous FBI shootout in Miami, in 1986, when agent Jerry Dove shot Michael Lee Platt with a 9mm pistol. The 115-grain Winchester Silvertip bullet stopped short of Platt’s heart, and he continued to fight. Ultimately, two FBI agents where killed and five more were wounded, and the supposed failure of one 9mm bullet spawned the FBI’s rigorous ammunition testing protocol. Ultimately, this led to the FBI’s adoption of the 40 S&W.

That’s the foundation of the debate. But is the 40 S&W really better than the 9mm? And if so, why did the FBI switch back to the 9mm? Let’s settle things with a full breakdown of the 9mm vs 40 S&W question.

40 Smith & Wesson Overview

The 40 S&W is a great pistol cartridge, but when law enforcement abandoned it, most everyone else did too. Richard Mann

After the Miami shootout, extensive FBI testing resulted in their adoption of 10mm pistols for general service. The 10mm ammunition they chose was a downloaded 180-grain bullet at about 950 fps. Many agents felt the issued S&W Model 1076 pistol in 10mm was too big and heavy, and as a result, the FBI switched to the 40 Smith & Wesson in 1997. When the FBI made the switch, so too did almost every law-enforcement agency in America. Suddenly, the 40 S&W was everywhere.

Civilians bought 40 S&W pistols too, partly because the 40 bridged the gap between the 9mm and the 45 Auto, but also because of the 1994 Federal Assault Weapons Ban that limited semi-automatic pistol magazines to 10 rounds. Because the 40 would work in 9mm-sized handguns, the 9mm Luger lost its higher-capacity advantage. From its introduction until 2015, the 40 S&W was one of the most popular pistol cartridges available. Then, almost overnight, it vanished.

The 9mm Luger Overview

Most police agencies now issue 9mm pistols, and 9mm is also the most popular pistol chambering for personal protection. Richard Mann

When the 40 S&W was introduced in 1990, the 9mm Luger cartridge was almost a century old. During those 90 years it had become very popular with law enforcement and civilians, but there’d been a long standing debate whether fast and light 9mm bullets were better than slow and heavy bullets fired by the 45 Auto. After the Miami shootout, 45 Auto lovers said, “I told you so.” But with the introduction of the 40 Smith & Wesson in 1990, the 9mm vs 40 S&W argument erupted and raged for nearly 25 years.

The ammunition developments that resulted from that shootout soon elevated 9mm performance. Bullet engineers learned how to leverage the high muzzle and rotational velocity of bullets fired from a 9mm pistol to enhance terminal performance. By 2015, focus had shifted to shootability, and the FBI realized that their agents shot 9mm pistols better than 40 S&W pistols. So, they reverted back to the 9mm and the improved ammunition for it. As the FBI goes, so too does most everyone else, and today the 9mm Luger is the most popular pistol cartridge in America and worldwide.

Related: Best 9mm Ammunition

9mm vs 40 S&W: Capacity Comparison

Statistics show that capacity matters in law-enforcement encounters. Richard Mann

When comparing guns of the same size, like a Glock 19 and a Glock 22, the 9mm pistol will hold 26 percent more ammunition compared to the .40 S&W. But how much does capacity matter? Statistics show that in most civilian self-defense encounters where a handgun is used, it rarely matters at all. However, in a law enforcement, capacity can be a big deal. Not just in terms of the amount of ammo the gun’s magazine can hold, but also in the amount of ammo an officer can carry. Three Glock 19 magazines hold 57 rounds of 9mm, while three Glock 22 magazines hold only 45 rounds of 40 S&W. Also, with the expiration of the 1994 Crime Bill, the 10-round magazine restriction is no longer a thing. Up until then, 10 rounds of 40 S&W seemed better than 10 rounds of 9mm Luger. But the smaller diameter Luger cartridge has now regained its capacity edge, and a lot of shooters like the idea of a pistol that holds more ammunition.

Winner: 9mm Luger

9mm vs 40 S&W: Terminal Performance

High-performance 9mm ammo like this shaves the difference between the 9mm and the 40 S&W hair thin. Richard Mann

Semi-auto pistol cartridges simply do not have the velocity to substantially damage tissue beyond the diameter of the hole the deformed bullet makes. To see that type of damage, bullets need to impact substantially faster. Because of this, the frontal diameter of the upset bullet matters. When bullets of the same type are compared, 0.40-caliber (10mm) bullets tend to upset with a wider frontal diameter than 9mm (0.355-caliber) bullets. Of course, the larger the frontal diameter of the deformed bullet, the harder it is for the bullet to penetrate.

Still, today’s ballisticians craft defensive handgun ammunition—regardless of caliber and cartridge—to perform well in the FBI’s testing protocol, which stipulates penetration of between 12 and 18 inches. This means that the terminal performance of good 9mm Luger and 40 S&W ammunition will be very similar, but in most cases 40 S&W loads will create a crush cavity that’s 10 to 20 percent larger in volume. On the other hand, some 9mm loads outperform 40 S&W loads when encountering the intermediate barriers that the FBI includes in their testing. Here’s a breakdown of the 9mm vs 40 S&S in terms of terminal ballistics:

Richard Mann

Winner: The 40 S&W may technically has a slight advantage, but for all practical purposes, it’s a tie.

9mm vs 40 S&W: Recoil/Shootability

Heavy-bullet 40 S&W loads like this make big holes, but they come with stiff recoil. Richard Mann

The shootability of 9mm pistols was one of the major considerations that led the FBI to return to it as an issue sidearm. Recoil complicates shooting no matter your experience level. Depending on the loads compared, the 40 Smith & Wesson will recoil with between 10 and 40 percent more force than the 9mm Luger. I’ve conducted a lot of testing to determine how recoil impacts pistol shootability, and I’ve discovered that a reduction in the speed at which accurate follow up shots can be made is directly proportional to any increase in recoil. The added recoil is the price you pay to get the 40 S&W’s marginally better terminal performance.

Winner: 9mm Luger

Make Mine a Nine

It’s hard for the 40 S&W to compete with the variety, compactness, and capacity of modern 9mm pistols. Richard Mann

Countless studies have shown that the effective difference between the 9mm Luger and the 40 S&W is not as large as initial testing data suggested. It’s also an established fact that the 9mm can be relied upon to save your life. Let’s not forget how Alaskan hunting guide Phil Shoemaker stopped a charging grizzly with his 9mm pistol. It’s not often that think a government agency gets it right, but in this case, I think the FBI did. With the nominal difference in terminal performance, hedging your bets on pistol that’s easier to shoot faster and more accurately seems like a solid pragmatic decision.

There are more 9mm pistols to choose from, three times the number of factory 9mm loads offered, and more inexpensive 9mm ammunition options available. The 40 S&W is now lost as the middle child between the 9mm and the 45 Auto. A quality pistol chambered for either cartridge can serve you well, but in the end, you can make mine a nine.

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