Can someone explain why a 6.5 mm caliber is a bullet diameter of 0.264" in the standard unit system? Since the metric to standard conversion is 25.4 mm = 1 inch, I keep getting that a 6.5 mm bullet should be 0.256". Am I missing something on bullet dimension measurements? I'll confess to not having any experience in handloading and I'm certainly no expert in cartridge construction.