Having had the sheer pleasure of flying BO' and BK's.....and the occasion to be left alone to my temptations.....I could never bring myself to roll or loop them.....I always chickened out first.
Far too many years of flying Bell Products I suppose.
Sikorsky 53's and 97's used to do those maneuvers and some have been on video.
A Bristow 58T went inverted coming off a Platform one night (based upon the Cabin Attendant's comment about walking on the overhead)...and the Pilot not knowing the actual attitude of the aircraft....but the Pitch Change Link knuckles on the Swash Plate gave evidence to the Jury to confirm something interesting happened.