Just think about it, your 14.5" is made for close quarters combat, not exchanging sniper fire from hilltop to hilltop.
If you want long range at least go with a heavier bullet. A 75g bullet might only be loaded to about 21g of H335 and will have a MV of 2450 fps but will drop only 120" @ 600 yards. Heavier bullets will drop less than light ones when you get into those long distances. They are also less prone to wind drift.