Yup. That’s right. The wrist busting .500 S&W wasn’t enough. This guy has a .600 NE single action revolver aka Zeliska Revolver built by Pfiefer Firearms. You can read more about the Zeliska Revolver here.
You can also read a Field & Streams article about why the guy had it built HERE. I wonder why he didn’t go for a .700 NE?
This one remains a fantasy gun because it’ll never be one that I would want to shoot.
910mm Man's Guy Stuff 
Where did you get this .600NE built and What do they go for?
I updated the post on the where it was built. How much do they go for? About $14K Euro which I suppose is around $21K USD.