Rainier Arms AR-15 5.56/.223 Precision Match Grade BCG Black Nitride Small. 56 Nitride is machined and finished to a higher standard to meet and exceed all Mil Spec. It is machined using the most precise equipment in the industry. The bolts are MPI/HP tested & Marked to give you ultimate confidence in your weapon system. Specifications for Rainier Arms AR-15 5.56/.223 Precision Match Grade BCG: Manufacturer: Rainier Arms Color: Black Finish: Nitride Fabric/Material: Steel Bolt Material: Steel Caliber: .223 Remington Gun Make: AR Platform Gun Model: AR-15 Hand: Right Package Contents: Rainier Arms AR-15 5.56/.223 Precision Match Grade BCG What firearm models does the manufacturer say Rainier Arms AR-15 5.56/.223 Precision Match Grade BCG is compatible with? The manufacturer says that Rainier Arms AR-15 5.56/.223 Precision Match Grade BCG is compatible with AR-15Rainier Arms RA-PMG-BCG-NITRIDE: AR-15 5.56/.223 Precision Match Grade BCG Black Nitride Small