ODIN Works LOW Mass 223 Nitride Bolt Carrier Group BCG for AR15/M4 .223/5.56mm Steel Black NSN N. This BCG has been significantly lightened weighing in at only 9 ounces it dramatically changes the amount of mass reciprocating in your gun. This BCG also features a Salt Bath Nitride finish that is both slick and durable. The carrier is made from 8620 steel and the bolt from 9310 steel. Bolt Carrier Group BCG fits AR15/M4 compatible style Rifles (i.e.) .223/5.56mm .300 Blackout. This is a HP or High Performance part. It will change how your rifle feels and shoots. Tuning may be required to make the gun properly run with this part. This can be done via the gas system or the buffer system. Specifications for ODIN Works LOW Mass 223 Nitride Bolt Carrier Group (BCG) for AR15/M4: Manufacturer: ODIN Works Color: Black Finish: Nitride Carrier Material: 8620 Steel Bolt Material: Steel Caliber: 5.56x45mm NATO .223 Remington Gun Model: M4 AR-15 Condition: New Package Contents: ODIN Works LOW Mass 223 Nitride Bolt Carrier Group for AR15/M4 What firearm models does the manufacturer say ODIN Works LOW Mass 223 Nitride Bolt Carrier Group (BCG) for AR15/M4 is compatible with? The manufacturer suggests that ODIN Works LOW Mass 223 Nitride Bolt Carrier Group (BCG) for AR15/M4 is compatible with AR-15 M4ODIN Works ACC-223-BCG-LM: LOW Mass 223 Nitride Bolt Carrier Group for AR15/M4 .223/5.56mm Steel Black NSN