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.

What, exactly, makes the Five-Seven different from other handguns?

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.

The P90 – like a competing personal defense weapon design, the 4.6mm Heckler & Koch MP7 – is supposed to pack more punch than submachine guns that fire a standard pistol rounds (9mm, say, or .45). And personal defense weapons are supposed to be capable of penetrating some kinds of body armor. As it happens, the Infantry School at Fort Benning, Georgia, has been mulling the requirements for a personal defense weapon for a few years now, although it's far from clear the Army would procure a weapon built around a new cartridge.

I've seen a range demo of the MP7, and it can indeed punch through a "soft" vest or a Kevlar helmet (whether it could penetrate SAPI plates is a different matter). 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.

[PHOTO: Wikimedia]

See Also: