I would like to interject the size and shape of the .416 Rigby case into the argument: .589" head size, 2.90" length overall and a 45 degree shoulder angle.
I have not seen one that did not feed well (of course I am not the warranty repair point for same).
I resisted the .300 WSM and .300 SAUM , but I intend to give the .300 RCM a test drive. It has some virtues for me.
jim