Leftover-The dimension I was speaking of is the distance between the case head and the top of the shoulder. As I don't have an actual case to measure, I am looking in Accurate Arms reloading manual #2 for a reference.
According to them, this distance is 1.76 inches.
Same book in 308, this distance is 1.56 inches.
IIRC, the first digit to the right of the decimal point is tenths, no?
I see my mistake-should have said length instead of diameter. Sorry-been running a bad fever for a few days!