Bolt is made of Mil-spec Carpenter 158 steel, Shot peened, High pressure tested and Mag Particle Inspected.  

Gas key is machined out of bar stock, nickel boron coated, and secured with grade 8 fasteners and staked per mil-spec. 

Full Auto Profile nickel boron coated 8620 Steel Bolt carrier is laser engraved with the PSA logo.

Link to parts manufacturer