Are you sure you bought the correct model? They sell a Mil Spec and a Commercial version which fit different sized tubes.
Basically the friction lock doesn't reduce wobble. Definitely have milspec version of both. Found this video for a fix on a PTS version so I think I'm going to try this, should be similar for a Magpul version I would think.
https://www.youtube.com/watch?v=9VX5XCQkcYc