Just who the *** do you think you are?

That would be diameter, not radius. 6.5mm is roughly the equivalent of .25 Caliber, and was a fairly popular rifle caliber in European countries in the early 20th century. In this case the bullet was a 6.5x52 Carcano fired from an Italian military rifle. The 6.5mm caliber is still popular today in the forms of 6.5 Grendel and 6.5 Creedmoor, for use with the AR platform.