From what I can see, you get a long shot bonus when killing an enemy past a very specific range regardless of your gun. (Like what, 200m?)
I suggest this bonus takes into account weapon range. I've hit some 100m+ kills with the Honey Badger, a gun that really isn't meant to kill at that range. A reward for killing outside of your weapons effective range will help alleviate the grind slightly while rewarding the player for a skilled kill.