I paper patch conicals. When the bullet exits the barrel the patching material needs to come off the bullet. if the patching material stays on for some or all of the flight that will affect accuracy.
If your barrel is .509 then you could find paper that is .004 or so but you want paper with some cotton content.
My 500 S&W bullets are .506 to .508 after wrapping dry no sizing. I bet they would work. Here is a link for some paper. Ron

http://www.buffaloarms.com/paper_pat...spx?TERM=paper