Can't go wrong with the dd bcg - Daniel Defense Bolt Carrier Group (BCG) Complete 5.56mm NATO

This BCG is being used in my custom DMR rifle build and it works flawlessly, as to be expected from Daniel Defense. I trust their products so much that any build includes at least the BCG and/or their barrels because they're such high quality. DD also has one of the best warranties in the business. Trust your builds - and your life - to Daniel Defense.