Another trick that works is to cut a few strips of 600 grit wet/dry sand paper to place in the ring halves. The strips should be slightly narrower than the rings and when placed in the ring half radius, slightly shorter than the ring half. Place one on bottom and one on top with the grit side towards the ring. The paper backing will provide a good friction fit. Some ring I have gotten actually come with some friction paper to do this very same thing. I can't remember which rings they were but I think they were burris. Hope this helps
Bret