FailZero M16/M4 EXO Nickel Boron Bolt Carrier Group 5.56 NATO Black

The FailZero M16/M4 EXO Nickel Boron Bolt Carrier Group is a fully assembled AR-15 bolt carrier group for 5.56x45mm NATO and .223 Remington rifles. It is intended as a drop-in replacement for the bolt carrier in a Mil-Spec upper receiver chambered for these calibers.

The carrier is made of steel with a Black Nitride finish, and the critical parts are coated with EXO Nickel Boron, which the listing describes as providing dry lubricity, wear resistance, and corrosion resistance. The black exterior is non-reflective. The firing pin has a chrome finish.

The extractor assembly includes a heavy spring, silicone insert, and o-ring, which the listing says improves extraction tension. The group fits most properly chambered Mil-Spec upper receivers.

• Platform: AR-15
• Calibers: 5.56x45mm NATO, .223 Remington
• Material: Steel
• Finish: Black Nitride with EXO Nickel Boron coating
• Firing pin finish: Chrome
• Color: Black
• Fits: Mil-Spec AR-15 upper receivers (5.56/.223 chambered)