This is from the article on Assault Rifles and their Ammunition on my website:
"This is the 6.8x43 Remington SPC (Special Purpose Cartridge) which fires a 115 grain bullet at 2,650 fps from a 16.5 inch barrel (7.45g at 808 m/s = 2,430j); very similar to the 'ideal' 6.85mm listed above. The cartridge case is based on the old .30 Remington commercial round, with a larger diameter than the 5.56x45 to increase the case capacity. This round develops 55% more muzzle energy than the 62 grain SS109/M855 loading at the muzzle, rising to 84% better at 550m due to its superior ballistic coefficient. The trajectory precisely matches that of the 7.62x51 ball out to 500m, and is only 10cm low at 600m."
I think it would probably run out of puff by about 800m. 2,000m shooting calls for the .50!