A number of off-the-record sources have told reporters that it was the Heckler & Koch 416 carbine rifle that was used to kill maniac-terrorist Osama bin Laden.
Popular Mechanics (PM) has published some interesting photos of the HK416, which it calls "the world's newest celebrity weapon." While the Pentagon and HK won't admit the gun's role in the now infamous raid on bin Laden's compound, PM says its use has become "accepted history":
It is undoubtedly true that U.S. special forces helped create and use this weapon, making it a logical choice for the Naval Special Warfare Development Group operators who swept bin Laden's compound in Abbottabad, Pakistan.
PM goes on to share some fun facts about the weapon:
German weaponmakers designed the HK416 specifically for, and with input from, U.S. Army special forces. Ten years ago, they wanted a better gun than the M4, which has a reputation for jamming. (There are those who defend the rifle, but U.S. special forces wanted something different.) The M16 and M4 both use gas tubes...and keep these gases (along with burned carbon particles) inside the gun, fouling the receiver. The HK416 uses a gas piston instead of a gas tube...This method allows the weapon to vent hot gas and burned carbon from the rifle with each shot...
The rifle can fire 800 rounds per minute, but SEALs on a raid would set the rifle to single fire, picking their shots carefully and conserving ammo. It's a shame that I can't pop off a few rounds myself to get the full experience. The techs tell me the kick is remarkably minimal, courtesy of a recoil pad in the butt stock.
If you're interested in more, click here to check it out.
UPDATE: The Military Times has a helpful graphic that graphically explains how the gas piston system works: