Ammo and ballistics 2 by Bob Forker has the 240 grain slug still going at 640 feet per second at 800 metres, that is the muzzle velocity of some pistol cartridges at the muzzle with much lighter bullets, so like I said I wouldn't like to be on the end of one at 1000 metres..
From wikapedia.
Firearms expert Julian Hatcher studied falling bullets in the 1920s and calculated that .30 caliber rounds reach terminal velocities of 90 m/s (300 feet per second or 204 miles per hour).[7] A bullet traveling at only 61 m/s (200 feet per second) to 100 m/s (330 feet per second) can penetrate human skin.[8]
