Not incouraging anyone to violate the minimum caliber (if one exist) when it comes to to size but a 6.5x55 in the correct location with a suitable bullet beats a .500 NE in the wrong location any day of the week.
Also Big Bore would depend on whether you define it as starting at .400 or .450.
Also Big Bore would depend on whether you define it as starting at .400 or .450.