From Above ^^^^^^^^
"Compare the O D at the bases and shoulders. UIM the 8mm is larger Around."
There is NOT as much diff as I thot. It looks a little larger due to the 8mm neck compared to 7mm neck.
7X57 - Base OD = .471
8X57 - Base OD = .469
7X57 - Shold OD = .431
8X57 - Shold OD = .434
Jerry