The Faxon Firearms 458/ 450 M16 Bolt Carrier Group gas key is staked.
The "458" in the name of this BCG refers to .458 Socom which this BCG is compatible with. The BCG is not compatible with other .458" caliber cartridges.
This BCG is made to Mil-Spec standards for upper compatibility and the bolt is made to work with SAAMI spec chambered barrels. Due to the variability of tolerances between manufacturers, specific fit to a barrel or upper is not guaranteed so we recommend checking headspace and fitment on any new build.