8x60N 8.07 mm = 0.317717 inch

8x60S 8.20 mm = 0.322835 inch

Looking over these two catalogs (also the bullet diameter info pages not shown in the scans) as well as one other DWM catalog from 1935, this is what I've pieced together:

8x60 N = .318" groove

8x60 S = .323" groove

8X60 Magnum Bomb = special higher velocity loading of the 8x60 S

Cheers!
-Bob F.