Just put a new bilever sir on my brand new RRA M4 upper. WHat a royal pain in the ass. I couldn't get the top piece to fit on properly and when I got it in place the screws for the piece in the delta ring wouldn't line up. I had to do some real fitting to get ti to work. I've had different model sir's on other uppers and installation was a breeze. I remember hearing something about RRA being out of spec. I wonder if this was the case here. Any feedback on your experience?

The top pic rail on OLDER RRA uppers (circa the '01 AR15.com limited edition) was indeed not to 1913 spec. Current units are, supposedly. I have mounted an ARMS product on my current-production RRA upper without issue. How old was the upper in question?

As far as I know it's brand new. Bought it here fron Big Bore