Hi, because Harlan Satrang at Triple River (e.g. the CZ Custom Shop) put it on for me. My rifle started out as a 375 H&H and Harlan changed it into a 500 Jeffery. At the time they were using almost all McGowen barrels on their Safari Classics. Not sure if they still are. You can call Jason at CZ USA or Harlan at Triple River if you have a U.S. built Safari Classic and they can tell you the barrel manufacturer. Both my original 375 (I still have the barrel if anyone needs one) and my 500 Jeffery shoot well under 1 MOA. The Jeffery shoots better.