Further Information

What really sets the newer versions of the ART system apart from the military ART models of the 1960's is the cam system which automatically allows for the trajectory of the round being shot.  Let's face it, the original ART scopes were set up to allow tactical shooters to keep hits on a man-sized target out to around 600 yards ... shooting rifles chambered for the U.S. military rifle cartridges of the time - the 5.56x45mm NATO (.223 Remington) and the 7.62x51mm NATO (.308 Winchester).

One of the things that made the M21 a successful sniping system during the Vietnam War was the ultra-simplistic means of range estimation that would also automatically adjust the scope for ballistic drop at whatever range the scope estimated the target to be at.