I currently have one of these turkeys. This is a model M-21i with a 4.2 MOA. It is mounted on a Meprolight Carry Handle adaptor. This sight is functionally useless in bright light (Arizona daylight). The dot is so washed out that it blends into the background. The handle adaptor would not work on the upper; the mounting stud was too short to start the locking leaver on the bottom. The upper was an FN manufactured A2. I really dislike this sight. I will not use it and intend to dump it cheep. Brand new in the box with warrenty not filled out.