I wish i read this thread before last night when i completed the directive. It took me awhile and it was super frustrating but i figured out aiming for the neck gains you a head shot. It was kind of a buzzkill after finally achieving my first auraxium directive.
Huh, upom further review, BASRs have a 2.1x headshot multiplier, for some stupid reason. That's why their OHK range turns out to be a bit further out than I calculated.
OHK range on the directive rifles is 265m last I checked. 300m on the Tier 3s, and (I think) 250m (it might be 245m, I can't remember at the moment) on the Tier 1s and 2s. I might be a bit off there, so correct me if I'm wrong!
