I think I know the problem. Is your barrel the heavy wall barrel?
It is probably the older clamp made for the older barrel diameter. The thicker barrels don't play well with the clamps. You can get the updated clamp from Nordic, or you can do what Nordic does yourself.
Put a large socket in the clamp and pinch it. I called Nordic and this the fix if you don't want to wait for them to send you a new one.
I don't remember the size socket that I used, but I believe if you look through my posts I've got the info on here somewhere.
ETA: The distinction on the part number to order is probably the retooling that Nordic did for the threads that were changed. Then OFM came out with a new heavy barrel, and that was another change. Two things that you need to keep in mind when ordering the Nordic stuff for the 930 platform.