Some of the M-223 mounts were out of spec and won't go on the rails. They're far too close together to slide on. I have had 2 like that and there are numerous others that have had the same problem. I'm unaware whether Nikon has fixed it yet or not. Just saying .......
There's a fine line between BRAVE ... and STUPID.
The two most important days in your life are the day you are born and the day you find out why.