Necromunda: Hired Gun

This can be easily done when paired with the Heightened Senses ability found under Cerebral Implant. The ability slows time giving you a chance to line up headshots with ease and the duration can be increased with upgrades. Personally I suggest using a shotgun for this and walking right up to enemies, but the long las is a good choice if you want to try this from a distance.

I did this at the arena. Get a gun single shot gun with a long scope, go far enough the the enemies trigger, go back up the ramp most of the way until it’s hard for them to shoot you and you can maneuver to shoot at their heads. They won’t follow as they can only go so far. They repopulate continuously and it took me less than a minute to finally get this one after trying in missions several times.