The bracket broke on my son's CM16 Raider 2.0 while playing airsoft - it cant be purchased except as part of a larger kit and due to the high stress on the part seems near impossible to repair.  On my guns, this is an exact fit replacement.

I print it vertically so the ring is orientated as a layer - this does mean the holes for the screws are a little fragile so be careful about over tightening them.  I attach it without brass inserts as I dont think there is the clearance to fit them - screws cut their own threads perfectly well in PLA or PLA+.