These are Revolver Supply Premium moon clips. They are designed to work in the S&W 929 8 Shot, chambered in 9 MM and 38 Super.

The normal moon clip thickness is 0.035″ and these are 0.040″ thick which makes the holding of the brass extremely tight.

The dimensional tolerance of the brass is large, so it is possible that all rounds might not work properly in your revolver.

But after you have sorted out all the offending rounds you will have the best fitting of a loaded moon clip possible.