Classic inertia feed. One thing that hasn’t been mentioned is lube on the feed lips. If they are oily or too slick, there is insufficient friction to hold the top round in place during recoil, especially if the mag spring is a little weak.
Wilson does recommend a little lubrication on their polymer follower though. A GI or Devel (Shooting Star) follower has so little contact surface inside the tube, I don't use any lube on those followers, but I do put a little on the CheckMate Patented Follower (CMF) as that has more contact area inside of the tube. Not a lot of lube, just a bit.