ORIGINAL: stubblejumper
ORIGINAL: GRIZZLYMAN
He might be referring to the measurement from center to center.
Which is the proper way to measure groups.
However I am wondering if 1/4" is his average group or his best group.I have fired an .080" group with one of my 300ultramags but the average group is 5/8".Therefore,I thereforecall it a 5/8" gun.
To get real technical, you measure outside to outside and subtract one caliber (in the case of the 30-06, you woulod subtract .308 inches) but it's basically the same thing.