All of these challenges involve shooting an entire clip into enemies without missing or reloading. I have done the similar "Perfectionist" with the sniper rifles, but that seemed so much easier with short clips and single fire. Since these challenges go all the way up to LMG I'm assuming that there must be some tips/tricks better than "don't die, don't miss". So what's the best strategy to complete these challenges?
You try using the Stability weapon proficiency on your LMG, AR and SMG. It reduces idle sway when aiming down site. I find I am able to get more bullets on target when using this proficiency.
Also, you could try using one of the 3 burst ARs (Type 95, M16A1) or the MK14 to complete the challenge related to ARs