I just came back from an elephant hunt with my Rizzini Rhino in .470 Nitro. While Rare Breed finds it to be unbearable, I have found it to be quite tolerable and enjoyed carrying it in the field. It was heavy at times, after longer walks, but not to the point of fatigue. I am 5' 9" and 185 lbs and assume that the factory LOP is more suitable to my build than those of taller stature, which may have been Rare Breeds issue. At one point on the sticks during target practice however, it did tend to give me bit of whiplash, but that was my own fault for not leaning into it properly. The following shot was not even nearly as felt as the first.
Beyond that, the regulation is incredible. This gun groups shots into the orange at 40 yards with the designated factory ammunition. It certainly is more capable than my abilities. When checking zero in Africa after travel, it shot 1/2" off the black bullseye at 40 yards off of sticks on the first shot...that was good enough for me and the PH. I can say that if you aren't in the market for a $20k double, I would not be afraid to look at the Rizzini Rhino Express in .470.
And I have never had a lick of trouble regarding doubling, loose forearm or any other mechanical issue.