HK, FMP and other G3 manufacturers produce Bolt Carriers from two pieces of steel and then weld them together.  Rhinemetall of Germany used one piece of solid billet and milled the bolt carrier as one part.  This process is more timely, costly and results in a stronger and superior bolt carrier which can survive more hard use and conditions than any other G3 Carrier.  Rhinemetall of Germany is not a small arms company like HK or FMP.  They concentrate on the production and development of tank cannons, heavy machine guns and heavy artillery.  When the German Government asked Rhinemetall to built G3 rifles they did, and the result was the finest G3 rifles and parts ever produced.