Who assisted the manufacturer that developed the ARC magazine for the gas-operated self-loading rifle with a rotating bolt?
TangoDown:  It developed the ARC magazine for the SCAR program with assistance from United States Navy SEALs. FN SCAR: The FN SCAR (Special Operations Forces Combat Assault Rifle) is a gas-operated (short-stroke gas piston) self-loading rifle with a rotating bolt.
United States Navy SEALs