It sounds like it'd be self-explanatory, kill a mech with one shot, but even hitting something with an AC20 round to a Commando's cherry red CT or cockpit doesn't seem to count towards the goal.
Edit: Apparently they just weren't registering or something. After restarting and going back in, I got the OSKs pretty quick. Or maybe my EBJ is just better than the champion Cicada. Damn Clan tech...(grumble grumble).
Edited by YaKillinMeSmalls, 27 August 2015 - 03:44 PM.