That is very interesting indeed. I'm still baffled this works fine in every action tried except the Nucleus. I wonder what ARC did so differently when they designed that action. Even works on the Mausingfield so seems very strange.
Cocking knob i believe extends a little longer than a standard rem 700. Bighorn went through this same lesson - their new laser engraved Tl3 wouldnt work with teh BnA tacsport so they released a lower sear. Why did ARC change the dimensions on the cokcing knob between the mausingfield and the nucleis ? F knows .. as the geissele worked fine in the mausingfield but didnt release the trigger in the nucleus (all 4) - anywaus Geissele adjusted these 4 triggers for me