http://en.wikipedia.org/wiki/SniperThe current world record for the longest range sniper kill is 2,430 meters (7,972 feet), accomplished by a Canadian sniper, Corporal Rob Furlong, of the third battalion Princess Patricia's Canadian Light Infantry (3 PPCLI), during the invasion of Afghanistan, using a .50 BMG (12.7mm) McMillan TAC-50 bolt-action rifle. This meant that the bullet had a flight time of ≈ 4.5 seconds, and a drop of ≈ 70 meters (230 feet).
This impressive feat of marksmanship is not typical for the effective range with a high first hit probability of the employed rifle (see Sniper rifle: maximum effective range). The ambient air density in the Shah-i-Kot Valley where Corporal Furlong operated is significantly lower than at sea level due to its 2,432 m (9,000 ft) mean elevation. This increases the maximum effective range of a high powered sniper rifle like Corporal Furlong used by ≈ 600 m (1968 ft).
The previous record was held by US Marine sniper Carlos Hathcock, achieved during the Vietnam War, at a distance of 2,250 meters.