I’ve taken a 14.5” KAC to 900 yards on E type silhouette with 69 grain GMM. However it’s not effective at that range. 5.56 generally has enough energy for useful terminal effect out to 500 or 600 yards depending on the ammo and barrel length. Some heavier bullets and longer barrels a can push that another 100 to 200 yards.
You are looking for the range at which the bullet retains between 250 Ft/lbs and 300 ft/lbs of energy.