According to an Australian newspaper, the record now stands at an amazing 1¾ miles!
Earlier this year [an Australian] Commando sniper team was secreted in Helmand. Through binoculars at a distance invisible to the naked eye they spotted a group of Taliban. The soldiers having means of identifying targets went through a process of obtaining verification and permission to engage.
Two marksmen using Barrett M82A1 50 calibre rifles simultaneously fired. The bullets were six seconds in the air. One killed the Taliban commander. It is not known for certain which sniper fired the fatal shot.
While there have been no triumphant press releases, in the tight global Special Forces sniper community the shot is much discussed, because it seems certain to be a world record.
As the bullet yawed through the thin air on a windless morning, GPS aids measured the distance at 2,815m [3,078½ yards]. That amounts to 2 1/2 times the length of the Sydney Harbour Bridge. The targeted Taliban would not have heard the gunfire.
The previous world record achieved by British Corporal Craig Harrison occurred also in Helmand in November 2009. Firing from a distance of 2,475m [2,706.7 yards], Harrison killed two Taliban.
There's more at the link.
That's an amazing achievement. Shots at that distance require a level of talent, practice and accumulated skill that's so high as to be almost unbelievable. A tip o' the hat to the Australian snipers concerned.