Beyond “Mil-Spec” the NEMO AR bolt carrier group is perfect for those who are looking for assured reliability with the best in coating technology. The bolt carrier group is the heart of your rifle. Selecting the best construction and coatings will ensure that you have lasting reliability and accuracy. – Case hardened 8620 steel bolt carrier nickel boron coated ground surfaces to meet exacting dimensional and surface finish tolerances – Case hardened 9310 steel bolt nickel boron coated magnetic particle inspected ground surfaces to meet exacting dimensional and surface finish tolerances – Hard chrome plated and ground firing pin – Nickel boron coated gas key staked 4130 steel – NIB coated cam pin – NIB coated extractor with spring rubber insert and o-ring support – Forward assist serrations