Went back and looked at Parashooter's chart. Then checked my SAAMI drawings. Parashooter's .064 is indeed correct for 303 British.
Calipers can be off that far off (.0655), hopefully your 303 gauge is correct. If you have a friend with a regular micrometer you may want to check the gauge. If your gauge does mike at .064 or a couple tenths on the high side you still should be good if it closes with minimal effort, talking about minor effort with your pinky. If your gauge is really .0655 then there is no question the headspace is correct.
Let us know what you come up with.