Upper receiver is fully machined from an aircraft grade 6061-T6 aluminum billet in a one piece design; Top picatinny rail is laser engraved for optic placement; Long stroke variable setting gas piston system; Three options for gas flow, and one for no gas flow; Charging handle is ambidextrous, non-reciprocating, foldable, spring returned and is easily relocated from left to right side without tools; 3 o'clock extractor position allows for easy swap between right and left handed shooting; Self-contained firing pin retention system enclosed in a rectangular bolt carrier that no longer requires a cotter pin; Recoil system does not extend beyond the upper receiver to fully operate allowing for easy install of a folding stock