Load chapter 16 return to deathshead's compound and after the beginning pickup all the ammo you can. Move on to a large open room (after killing a dog) and switch to dual wielding by pressing up on the d pad. You should have dual assault rifles, pistols, and AR Marksmans.
Kill everything until you run out of ammo, switch to the next dual set you have, and repeat until everything is dead. Press start and restart the last checkpoint you should be right outside the door. Repeat until you have all your kills. You should have the LKW kills just by going through the campaign normally, but if for some reason you didn't you can get those kills here too.