WMD results on a .50 caliber budget
 
I was actually searching for the Sitting Ducks posters when I stumbled across this study. I'm not sure who the Violence Policy Center is, but the report is an interesting read on how someone could wreak havoc with this weapon.
For what it's worth, I fired a 50-caliber machine gun in the Army. There wasn't a sight on it. The instructions were just to point it downrange in the vicinity of the truck-sized target, and when you see dirt kicking up, adjust accordingly.
According to the Geneva Conventions, this bullet was too large to be used against people, only equipment, such as a truck. The running joke was to aim at the equipment the enemy was wearing on their web belt.