When the FBI Ditched 9mm, Tried 10mm, and Came Back: The Full Story (2026)

Last updated March 18th 2026

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When the FBI Ditched 9mm, Tried 10mm, and Came Crawling Back

If the FBI endorses your ammunition, you sell a lot of ammo. If the FBI dumps your caliber, the market feels it. That’s the kind of influence the Bureau has on the American firearms industry, and the story of how the FBI went from 9mm to 10mm to .40 S&W and back to 9mm again is one of the most consequential caliber stories in modern firearms history. It directly created one cartridge (.40 S&W), killed another (10mm as a mainstream caliber), and ultimately validated 9mm as the undisputed champion of defensive handgun ammunition.

Here’s how it all went down.

The 1986 FBI Miami Shootout

On April 11, 1986, eight FBI agents engaged two serial bank robbers, William Matix and Michael Platt, in a gun battle in Dade County, Florida. What was supposed to be a routine felony stop turned into one of the most studied firefights in law enforcement history.

The details are brutal. Agents fired approximately 70 rounds. Platt and Matix were hit multiple times but kept fighting. Platt, despite being hit by a 9mm round that collapsed his right lung early in the fight, continued shooting and killed two FBI agents (Jerry Dove and Benjamin Grogan) before being killed himself. Five other agents were wounded.

The 9mm Winchester Silvertip round that hit Platt early in the fight stopped just one inch short of reaching his heart. That single inch changed the direction of American law enforcement ammunition for the next 30 years. The FBI concluded that their 9mm ammunition had failed to penetrate deeply enough to stop the threat, and they needed something more powerful.

The 10mm Auto Experiment

The FBI’s response was to adopt the 10mm Auto cartridge, originally designed by Jeff Cooper and manufactured by Norma. The 10mm is a genuinely powerful round: a full-power 10mm load pushes a 180-grain bullet at 1,300+ fps, generating over 600 ft-lbs of energy. That’s significantly more powerful than 9mm or .45 ACP. It smashes through barriers, penetrates deeply, and hits with authority.

The FBI adopted the Smith & Wesson 1076, a large-framed semi-auto chambered in 10mm. On paper, it was the answer to every complaint about 9mm’s terminal performance. In practice, it was a disaster for a large, diverse agency.

The problems were immediate:

• Recoil was too much. Full-power 10mm generates significantly more recoil than 9mm or .45 ACP. Many agents, particularly smaller-framed agents and those who didn’t shoot regularly, couldn’t manage it. Qualification scores dropped.
• The guns were too big. 10mm pistols are built on large frames to handle the pressure. The S&W 1076 was heavy and difficult to conceal for agents who needed to carry discreetly.
• The guns broke. The S&W 1076 had reliability issues, partly because the 10mm’s high chamber pressures were hard on the platform.

The FBI’s solution? Download the 10mm to a reduced-power load (sometimes called “FBI Lite”) that was more manageable. This downloaded 10mm pushed a 180-grain bullet at around 950 to 1,000 fps, which was ballistically very similar to what a .40 caliber bullet could do in a shorter case. Someone at Smith & Wesson noticed this and had an idea.

For more on where 10mm fits today, see our best 10mm pistols guide and our 10mm for bear defense article. The 10mm has found a great niche as an outdoors and hunting cartridge, even if it failed as a mainstream law enforcement round.

The Birth of .40 S&W

Smith & Wesson and Winchester realized that the FBI’s downloaded 10mm load could be replicated in a shorter case that would fit in a 9mm-sized pistol frame. In 1990, they introduced the .40 S&W cartridge: essentially a shortened 10mm that delivered the FBI’s preferred ballistic performance in a more compact, controllable package.

The .40 S&W was an immediate hit with law enforcement. It offered more power than 9mm (a 180-grain bullet at 985 fps vs 9mm’s 124-grain at 1,150 fps), fit in existing 9mm-sized frames, and was easier to shoot than full-power 10mm. The FBI adopted it. Police departments across America followed. By the mid-1990s, the .40 S&W was the dominant law enforcement caliber, and the Glock 22 in .40 became the most issued police pistol in America.

The .40 reigned for nearly 20 years. Then ammunition technology caught up, and the whole equation changed again.

The 2014 Return to 9mm

By the early 2010s, 9mm ammunition had evolved dramatically from the Winchester Silvertip that failed in 1986. Modern hollow points like Federal HST, Speer Gold Dot, and Hornady Critical Duty used bonded cores, engineered jacket designs, and advanced propellants to achieve consistent 12 to 18 inches of penetration through FBI barrier protocols with reliable expansion. These were not the same bullets that failed in Miami.

In 2014, the FBI’s Training Division published an internal report that essentially said: 9mm is now as effective as .40 and .45 in terminal performance, while offering less recoil, higher capacity, better agent qualification scores, and lower ammunition costs. The conclusion was unambiguous: there was no longer a performance justification for the .40’s additional recoil and reduced capacity.

The FBI adopted the Glock 17M and 19M in 9mm. The dominoes fell immediately. Department after department switched from .40 to 9mm. Used .40 caliber duty guns flooded the civilian market at bargain prices (which was great for buyers). And the .40 S&W began its slow march toward irrelevance.

For the full picture on why 9mm dominates today, see our why does everybody use 9mm guide. For the direct caliber comparison, see our 9mm vs .45 ACP and 9mm vs .40 S&W articles. And for the best modern 9mm ammunition, see our best 9mm ammo guide.

What This Means for Civilian Gun Owners

The FBI’s caliber journey matters for civilians because it validated 9mm as the objectively best defensive handgun caliber for most people. If the world’s premier law enforcement agency, with all its resources and testing capability, concluded that 9mm is as effective as larger calibers while being easier to shoot, that should carry weight in your own caliber decision.

The practical takeaways:

• 9mm with modern hollow points is more than adequate for self-defense. The bullets that failed in 1986 are not the bullets available today.
• .40 S&W is a dying caliber. It still works, but there’s no performance advantage over 9mm that justifies the recoil and capacity tradeoffs. If you already own a .40, keep shooting it. If you’re buying new, buy 9mm.
• 10mm has found its niche as a hunting, outdoors, and bear defense caliber where the extra power is genuinely useful. It’s not a mainstream self-defense round.
• Shot placement still beats caliber. The FBI’s own data shows that the single biggest factor in stopping a threat is accurate shot placement under stress, not bullet diameter or energy.

For choosing your own self-defense handgun, see our choosing a gun for self-defense guide. For the guns the FBI actually carries now, see our best Glock pistols and evolution of police handguns guides.

Related Guides

• Why Does Everybody Use 9mm?
• 9mm vs .45 ACP
• 9mm vs .40 S&W
• Best 9mm Ammo
• 12 Best 10mm Pistols
• 10mm for Bear Defense
• 11 Best Glock Pistols
• Evolution of Police Handguns
• Best Defensive Ammo
• 15 Best Concealed Carry Handguns

The Bottom Line

The FBI’s 30-year caliber journey, from 9mm to 10mm to .40 S&W and back to 9mm, is the most influential ammunition story in modern firearms history. It created the .40 S&W, popularized the 10mm, and ultimately proved that modern 9mm ammunition is all the stopping power most people need. The lesson is simple: technology changes, and the right answer in 1986 isn’t necessarily the right answer in 2026. Today, 9mm with quality hollow points is the proven, FBI-validated standard for defensive handgun ammunition.

FAQ: FBI and 9mm vs 10mm