It was the late 1980s. NATO was panicking. They weren’t worried about tanks or planes, specifically, but about Kevlar. Body armor was becoming standard issue for Soviet troops, and the 9mm Parabellum—the world's sidearm sweetheart—was suddenly looking like a Nerf dart against it. They needed something small, fast, and mean.
Enter the FN Herstal 5.7x28mm.
FN Herstal, the Belgian giants behind the legendary FAL and the M249 SAW, didn't just tweak an old design. They basically shrunk a rifle cartridge and shoved it into a handgun frame. It was weird. People laughed. Then they saw what it did to a CRISAT target (a titanium plate and 20 layers of Kevlar). Suddenly, nobody was laughing anymore.
The Secret Sauce of the 5.7x28mm
Why does this tiny caliber have such a cult following? Honestly, it’s physics. While a .45 ACP is like a slow-moving bowling ball, the FN Herstal 5.7x28mm is a needle. It’s light. It’s incredibly fast. Because the projectile is so light—usually between 27 and 40 grains—the recoil is almost non-existent. You can fire a Five-seveN pistol as fast as you can pull the trigger and the sights barely move. It’s cheating, basically.
But there’s a catch.
Velocity is the name of the game here. Out of the long barrel of a P90, the round screams. Out of a concealed carry pistol? It loses some of that "oomph." This is where the internet arguments start. Critics call it a glorified .22 Magnum. Fans point out that a .22 Mag is a rimfire cartridge prone to jamming, whereas the 5.7 is a centerfire, bottlenecked beast built for 100% reliability in combat zones.
Breaking Down the Ballistics
Let's talk about the tumble. Most bullets try to stay straight. When a 5.7x28mm projectile hits soft tissue, its center of gravity is so far back that it immediately wants to flip. It yawns. It tumbles. This creates a wound channel much larger than you’d expect from a bullet that looks like a sharpened pencil.
Specific loads matter a lot here:
- The SS190 is the duty round. This is the "armor-piercing" stuff that civilians generally can't touch. It uses a dual-core of steel and aluminum.
- SS197SR is what you’ll actually find at the local gun shop. It sports a blue polycarbonate tip and is tailored for target shooting or varmint hunting.
- Subsonic loads exist, but they’re kinda niche. If you take away the speed, you take away the 5.7's only real superpower.
Why Everyone is Making 5.7 Guns Now
For years, if you wanted to shoot FN Herstal 5.7x28mm, you had to buy an FN gun. And FN guns aren't cheap. The Five-seveN pistol famously looked like a "Blocky" Lego toy and cost a month's rent. For a long time, the caliber felt like a boutique luxury for people who watched too much Stargate SG-1.
Then the patents started expiring.
Suddenly, Ruger dropped the Ruger-57. It was half the price. Then Smith & Wesson jumped in with the M&P 5.7, using a cool gas-operated rotary barrel system. Even PSA released the Rock 5.7. This surge in hardware has actually made the ammo cheaper—or at least more available. We've moved from "the weird Belgian round" to a legitimate mainstream choice for home defense and competition.
The Elephant in the Room: Stopping Power
We have to be real. A 5.7x28mm will never have the raw "knockdown" energy of a .45 or a spicy 10mm. If you’re looking to stop a charging grizzly, please, use something else. However, for a defensive scenario, the logic is different. Would you rather have 8 rounds of .45 that kick like a mule, or 22 rounds of 5.7 that you can place with surgical precision under high stress?
Most people shoot the 5.7 better. Accuracy beats energy every single time.
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Real World Performance vs. Video Game Hype
If you play Call of Duty or Counter-Strike, you think the P90 is a laser beam that cuts through steel doors. In the real world, it's more nuanced. The Secret Service uses it because it’s compact and won’t over-penetrate through three suburban houses if they miss a shot. The bullet is so light that it tends to break apart or lose energy rapidly when it hits hard barriers like drywall.
That’s a feature, not a bug.
In 2026, we’re seeing a massive shift toward "PDW" (Personal Defense Weapon) braces and large-format pistols. The FN Herstal 5.7x28mm is the king of this category. It bridges the gap between a pistol and a carbine perfectly. You get 50-yard accuracy out of a package that fits in a backpack.
What to Look Out For
Buying into this caliber isn't all sunshine and low recoil. You need to be picky.
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- Ammo Sensitivity: Some of the newer, cheaper 5.7 pistols can be picky with certain loads. The FN original is still the gold standard for eating anything you feed it.
- The "Flash" Factor: Because there's a lot of powder burning in a short space, the muzzle flash can be intense. Shooting this at an indoor range will make you the loudest (and brightest) person in the room.
- Magazine Costs: Even though the guns got cheaper, the mags haven't. Expect to pay a premium for high-quality steel or polymer magazines that can handle the high spring tension required to feed these rounds fast.
The Practical Verdict
Is the FN Herstal 5.7x28mm a gimmick? No. It’s a specialized tool that finally found its market. It’s the perfect caliber for shooters who are recoil-sensitive, or for anyone who values capacity over raw mass. Twenty-plus rounds in a flush-fit magazine is a massive tactical advantage that’s hard to ignore.
The "Tactical Tuna" (the FN FS2000 or the P90) might have started the trend, but the modern era of 5.7 is about accessibility. Whether you're plinking at the range or looking for a lightweight setup for the truck, this caliber offers something 9mm simply can't: flat trajectories and effortless control.
How to Get Started with 5.7x28mm
If you're ready to jump in, don't just buy the first gun you see. Start by handling the Smith & Wesson M&P 5.7 and the FN Five-seveN MRD side-by-side. The ergonomics are wildly different. Also, start stockpiling ammo now. While prices have come down from the "two dollars a bang" nightmare of a few years ago, it’s still pricier than 9mm. Look for bulk American Eagle or Fiocchi packs to keep your training costs manageable. Stick to 40-grain V-Max loads for a good balance of price and performance, and always check your local laws, as some states have weird hang-ups about high-capacity magazines that make the 5.7's best feature—its volume—a moot point.
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