FBI field agents carry Hornady Critical Duty 9mm +P 135-grain FlexLock rounds in the Glock 19M pistol. That is the FBI duty ammunition currently issued to agents, and the choice reflects a long testing program that concluded modern 9mm hollow-points match larger calibers in terminal performance while letting agents shoot faster and more accurately. Tactical units add rifles and shotguns with their own ammunition, and training uses cheaper or specialized rounds depending on the drill.
What the FlexLock Round Is
Hornady lists the Critical Duty 9mm +P 135-grain FlexLock in its law enforcement catalog as “tested and selected by the FBI,” with performance data referenced against a 4.5-inch Glock 17 barrel.1Hornady. 2025 Hornady Law Enforcement and Military Catalog The bullet has a heavy jacket and a flexible polymer insert seated in the hollow-point cavity. The insert keeps debris out when the bullet punches through barriers like auto glass or sheet metal, so the round still opens up on the other side rather than plugging closed and behaving like a solid.
That barrier problem is what the FlexLock was engineered around, and it is central to why the FBI selected it. A hollow-point that expands well in bare tissue but fails after glass is not useful for agents who may have to fire through a windshield or a car door.
Why 9mm, and Why the Glock 19M
The Glock 19M is a compact 9mm pistol built to FBI specifications, and it is what new agent trainees learn on at Quantico.2Federal Bureau of Investigation. Becoming an Agent – Firearms Training It replaced the Glock 23 in .40 S&W, which had been standard issue through December 2016.
The FBI’s caliber history runs in a loop. Agents carried .38 Special revolvers and 9mm semi-automatics into the 1980s. After the 1986 Miami shootout, in which two suspects absorbed multiple hits and kept fighting long enough to kill two agents and wound five others, the Bureau decided its ammunition was not penetrating deeply enough to reach vital organs reliably. The response was a move to larger calibers, first 10mm Auto and then the shorter-recoiling .40 S&W.3Police1. How the FBI Reignited the Pistol Caliber War
The .40 S&W era lasted roughly two decades and had trade-offs. Sharper recoil made the round harder to manage, especially in the compact Glock 23 frames agents concealed. Around 2007, FBI researchers began noting that modern 9mm projectiles were performing essentially the same as .40 S&W in protocol testing. Bonded and barrier-optimized 9mm bullets, developed in part because manufacturers were designing to the FBI’s own standards, penetrated and expanded as reliably as the larger round.
When the Bureau tested its own workforce, from office personnel who rarely handled firearms to Hostage Rescue Team operators, six out of ten shooters were faster and significantly more accurate with 9mm. In July 2014, the FBI issued a solicitation for a new family of 9mm pistols, effectively closing the internal debate.3Police1. How the FBI Reignited the Pistol Caliber War The logic was simple. If terminal performance is the same, pick the caliber that lets agents hit more, shoot faster, and carry more rounds in the magazine.
The Testing Protocol Behind the Choice
The FBI Protocol is the standardized method the Bureau uses to evaluate handgun ammunition, and it has become the working benchmark for the law enforcement ammunition industry. It grew out of the post-Miami investigation. The protocol measures how a bullet performs in calibrated 10 percent ballistic gelatin, which approximates the density and resistance of human muscle tissue. To pass, a round must penetrate between 12 and 18 inches. Less than 12 inches risks failing to reach vital organs. More than 18 inches creates unnecessary over-penetration risk.
The harder part is the barrier testing. Ammunition must deliver consistent penetration and expansion after first passing through:
- Heavy clothing, multiple layers of fabric placed against the gelatin
- Thin mild steel simulating a car door
- Interior wallboard
- Structural plywood
- Laminated auto glass, angled to replicate a real windshield
A bullet that opens up beautifully in bare gelatin but pencils through after auto glass fails. The protocol also evaluates weight retention and accuracy from the specific firearms the agency issues.
What Tactical Units Carry
FBI SWAT and the Hostage Rescue Team operate in situations where a 9mm pistol is not the right tool.4Federal Bureau of Investigation. SWAT at 50 – FBI Tactical Teams Evolve to Meet Threats
Rifles
Tactical teams use Colt-pattern carbines chambered in 5.56mm NATO, essentially AR-15 variants.2Federal Bureau of Investigation. Becoming an Agent – Firearms Training The round has low recoil, a flat trajectory, and effective terminal performance at typical engagement distances. HRT also fields precision rifles chambered in .308 Winchester (7.62mm NATO) for longer-range work. The heavier round carries more energy at distance and defeats barriers that 5.56mm cannot.
Shotguns
The Remington 870P, a pump-action 12-gauge, is part of the standard arsenal. Ammunition includes buckshot for close-range engagements and slugs for more precise shots at moderate distances. The shotgun also handles breaching tasks that rifles and handguns are less suited to.
Less-Lethal
Tactical teams carry less-lethal munitions as well. The most common are 12-gauge bean bag rounds, flexible pouches filled with lead shot that incapacitate through blunt impact. Some agencies use 40mm sponge rounds fired from dedicated launchers, which offer more accuracy at greater distances than bean bags.
Training Ammunition
The FBI uses different ammunition depending on what the training is meant to do, because duty hollow-points are expensive and not always the safest option for the range environment.
For general marksmanship practice, agents fire full metal jacket rounds. FMJ is significantly cheaper than duty hollow-points and gives similar recoil and point-of-aim characteristics, though it does not expand on impact. Duty ammunition is typically reserved for qualification. Agents fire a 50-round course of fire at distances from 3 to 25 yards under time pressure, and the passing threshold is 80 percent.
Indoor ranges add a ricochet problem that FMJ cannot solve. Frangible ammunition, made from compressed metal powder rather than a solid lead core, disintegrates into dust on contact with steel backstops or concrete walls. That makes it much safer for close-range work in enclosed spaces.
The most demanding training uses marking ammunition, commonly known by the brand name Simunition, which fires paint-filled plastic projectiles from modified versions of standard-issue weapons. On impact the round leaves a colored splatter, giving immediate feedback on shot placement.5Federal Bureau of Investigation. Simunition Training Weapons designated for marking rounds are painted orange on the slide and magazine floor plate to prevent confusion with live firearms.6FBI Law Enforcement Bulletin. Focus on Training – Training for Deadly Force Encounters Force-on-force scenarios with these rounds are where agents work through the decision-making stress that a flat range cannot replicate.
Can Civilians Buy the Same Round?
The exact Hornady Critical Duty 9mm +P 135-grain load the FBI carries is commercially available in most states. The only difference between the Bureau’s supply and retail stock is packaging. The FBI receives 50-round boxes, and retail comes in 25-round boxes. There are no restricted components or special formulations in the FBI’s duty load. Hollow-point ammunition is legal for civilian purchase in the vast majority of states, though a handful impose restrictions on possession or carry.
The FBI Protocol has become the standard that most major manufacturers design defensive ammunition around, so the testing regime built after a 1986 gunfight now shapes the performance of rounds sold to civilians and police departments alike.3Police1. How the FBI Reignited the Pistol Caliber War