Why the FBI Ditched 9mm for .40 S&W — Then Switched Back
In This Guide
The FBI adopted 9mm, abandoned it after a catastrophic gunfight, spent 28 years chasing bigger calibers, and then came back to 9mm — admitting the whole detour was based on flawed conclusions about a single bullet failure. This is the most consequential ammunition decision in American law enforcement history, and it reshaped what every concealed carrier, police department, and gun manufacturer prioritizes.
April 11, 1986: The Shootout That Changed Everything
Eight FBI agents intercepted two serial bank robbers — Michael Platt and William Matix — in a residential area of Miami-Dade County. What followed was a four-minute gunfight with an estimated 119–130 rounds fired. When it was over, Special Agents Benjamin Grogan and Jerry Dove were dead, and five other agents were wounded. Both suspects also died, but not before Platt — despite sustaining a wound early in the fight that would have eventually been fatal — continued shooting for several minutes and killed both agents.
The bullet that triggered a 28-year caliber debate was a single 9mm 115-grain Winchester Silvertip hollow point fired by Agent Dove. It struck Platt in the right upper arm, penetrated through the arm and into his chest, and stopped approximately one inch short of his heart. The bullet had expanded as designed and simply ran out of penetration depth. Platt, despite what was ultimately a fatal wound, continued fighting with devastating effectiveness for the remaining minutes of the battle.
The FBI's conclusion: 9mm didn't have enough stopping power. In hindsight, the more accurate conclusion would have been that the specific bullet they chose — a lightweight 115-grain hollow point that prioritized expansion over penetration — failed to penetrate deep enough. The caliber wasn't the problem. The bullet design was.
The 10mm Experiment
In the aftermath of Miami, the FBI convened wound ballistics panels and developed what became known as the "FBI Protocol" — a standardized testing methodology that remains the gold standard for defensive ammunition evaluation. The protocol requires 12–18 inches of penetration in calibrated ballistic gelatin through various barriers (clothing, auto glass, plywood, drywall, sheet metal).
Their initial answer was the 10mm Auto. It delivered the penetration and energy they wanted. But there were two immediate problems: the recoil was punishing (far beyond what the average agent could control effectively), and the only available pistols were large-frame designs too bulky for everyday concealment.
The FBI's solution was to download the 10mm — reducing the powder charge to produce more manageable recoil. This "FBI lite" 10mm load pushed a 180-grain bullet at 900–1,000 fps instead of the full-power 1,300+ fps.
The Birth of .40 S&W
Smith & Wesson and Winchester recognized something clever: if the FBI's downloaded 10mm load used less powder and left airspace in the case, why not shorten the case to eliminate that airspace? The shorter case would fit in medium-frame 9mm-sized pistols instead of requiring the large-frame 10mm platforms.
The result, introduced in 1990, was the .40 Smith & Wesson — ballistically identical to the FBI's reduced-velocity 10mm load but packaged in a shorter cartridge that worked in compact pistols. The FBI formally adopted the Glock in .40 S&W in May 1997.
Law enforcement followed the FBI's lead en masse. By the early 2000s, the .40 S&W was the dominant law enforcement caliber in America. The California Highway Patrol adopted it. Hundreds of departments followed. The cartridge became the default answer to "what caliber should police carry?"
The Problems Nobody Talked About
The .40 S&W delivered on paper. In practice, three problems emerged over two decades of field use:
Reduced accuracy under stress. The .40 S&W produces noticeably snappier recoil than 9mm in comparably sized pistols. In controlled range conditions, trained shooters handle it fine. Under the stress of an actual gunfight — where law enforcement officers miss 70–80% of shots fired, according to the FBI's own data — the additional recoil measurably degraded hit rates. More misses means more rounds flying into backgrounds. The FBI determined that the hits you land matter more than the energy of the hits you miss.
Lower capacity. A Glock 17 holds 17 rounds of 9mm. A Glock 22 holds 15 rounds of .40 S&W. That's two fewer rounds in the same-sized frame. In a gunfight where most shots miss, those two rounds matter.
Accelerated wear. The snappier recoil impulse of .40 S&W accelerated frame and slide wear on duty pistols. Departments reported higher maintenance costs and shorter service life on .40 caliber pistols compared to their 9mm predecessors.
The 2014 Return to 9mm
Around 2007, FBI Ballistic Research Facility (BRF) researchers noticed something remarkable: modern 9mm defensive projectiles were performing essentially identically to .40 S&W loads in FBI protocol testing. By 2010, the conversation about switching back to 9mm was getting serious internally.
The FBI's BRF, led by supervisory special agent Jason Scott, published a 200-page internal study in June 2013 making the case for returning to 9mm. In 2014, the FBI officially announced the switch. The decision was based on three findings:
Modern 9mm JHP matches .40 S&W terminal performance. Advances in bullet engineering — specifically the development of bonded cores, controlled-expansion jackets, and optimized velocity windows — had closed the performance gap entirely. The Speer Gold Dot G2, which the FBI ultimately selected as their duty load, delivered penetration and expansion in FBI protocol testing that equaled or exceeded their .40 S&W loads.
Agents shoot 9mm more accurately. Better hit rates in rapid-fire strings, less recoil-induced flinch development, and faster follow-up shots. When you combine this with the fact that shot placement is the primary determinant of stopping a threat (not caliber energy), 9mm's shootability advantage translates directly to better outcomes.
Higher capacity and lower cost. More rounds per magazine, cheaper training ammo, and less wear on duty weapons. As FBI BRF's Scott stated directly: the switch was not about saving money — it was about making agents more effective in gunfights. The cost savings were a bonus.
The Quote That Settled the Debate
When Dave Emery at Hornady was asked by the FBI why 9mm had improved so much compared to larger calibers, his answer was illuminating: manufacturers could engineer 9mm bullets at higher velocities while maintaining reliability across a fleet of guns. That extra velocity window allowed them to design projectiles that performed more consistently through barriers. His conclusion: there's minimal practical difference between the two calibers with modern ammunition.
What Actually Changed: Bullet Technology
The 9mm of 1986 and the 9mm of 2014 share a caliber designation and almost nothing else. The 115-grain Silvertip that failed in Miami used a simple cup-and-core construction — a thin copper jacket crimped around a soft lead core. It expanded aggressively (which was considered a positive) but at the cost of penetration depth.
Modern defensive 9mm — Federal HST, Speer Gold Dot, Hornady Critical Duty — uses fundamentally different engineering. Bonded cores prevent jacket-core separation. Engineered expansion cavities control mushroom diameter precisely. Cannelures and jacket skiving ensure consistent petal formation across a wide velocity range. The result is a bullet that expands reliably through barriers (heavy clothing, auto glass, drywall) while still reaching 14–18 inches of penetration in gelatin.
The irony is profound: the FBI spent 28 years and untold millions pursuing bigger calibers because of a single bullet failure — and the solution was never a bigger bullet. It was a better bullet in the original caliber.
What This Means for You
The FBI's journey validates a simple truth for concealed carriers: with modern premium defensive ammunition, 9mm is as effective as .40 S&W or .45 ACP for self-defense, while offering less recoil, higher capacity, and lower cost.
That doesn't mean .40 S&W or .45 ACP are bad choices — they're excellent calibers with proven track records. But if you're choosing a defensive caliber today, the argument for anything other than 9mm has to overcome the combined advantages of shootability, capacity, and ammunition availability.
If the FBI — an organization that literally invented modern terminal ballistics testing because they lost agents in a gunfight — concluded that 9mm is optimal for their agents' lives, that carries significant weight.
For our recommended defensive 9mm loads, see our best 9mm self-defense ammo guide. For current prices, check the 9mm deals page.