What is an FN Five-Seven?

The FN Herstal Five-Seven is a fairly ordinary pistol chambered for a quite unique cartridge. The 5.7X28mm round is reminiscent of the AR15/M16 5.56X45mm cartridge (also known as the .223 Remington) adopted by the US military during the Vietnam War era. Like this rifle round, it uses a smaller than normal projectile fired at high velocity. The projectiles are very similar in size, with the 5.7X28 bullet weighing about the same as light .223 bullets intended for varmint (small game) hunting.

What, Exactly, Is a ‘Cop-Killer’ Gun? (Updated) | Danger Room | Wired.com:
"News reports on the Fort Hood rampage say that the alleged shooter, Maj. Nidal Hasan, used an FN Herstal Five-Seven pistol — described in some reports as a “cop killer” gun.

. . .

The Five-Seven is chambered for the 5.7 x 28mm cartridge, ammunition originally developed by FN Herstal for the FN P90 Personal Defense Weapon. The P90 was conceived as a compact, powerful weapon that could be carried by aircraft crews, vehicle drivers and other troops who needed a weapon that was smaller than a carbine but larger than a pistol.

. . .

Gun control group The Brady Campaign says it bought and test-fired a Five-Seven, and that it successfully penetrated a police vest. That said, it doesn’t seem quite accurate to call the Five-Seven a pocket-sized assault rifle. Its barrel would give it a lower muzzle velocity than a PN90; likewise, it strikes me as unlikely that it would give a shooter much more accuracy and effective range than a standard pistol. And plain-vanilla pistol round can be devastating enough: Think of the Virginia Tech shooter, who used a Glock 9mm and Walther .22.

We don’t know at this point a lot of the details: Exactly what kind of ammunition the shooter used; how many shots in total were fired; and at what range. That will take a lot of police work, and a lot of patience.

Still, the tragedy at Fort Hood seems likely to renew debate: Both on gun control, and on the kinds of measures to protect troops while they are on base, and unarmed.

UPDATE: Hasan bought the gun on August 1st — less than a month after he was transferred to Ft. Hood, a law enforcement official tells Newsweek’s phenomenal new Declassified blog. “At the same time, Hasan also bought several high capacity 20 round magazines that allowed him to rapidly fire off multiple rounds during the attack without reloading, the official said."