I've completed over 350 rounds of Onslaught since Final Shape launched, 150 of those were on expert mode, but the Falling Guillotine has not dropped a single time, 80% of the drops I get are either Hung Jury or Midnight Coup. Am I just that unlucky or is there a rotation or something else I don't know of? I have gotten weapons I didn't have before final shape, so I don't think its because I didn't finish the quest for it.