Look at the diameter of the shoulder, compared to the base dia.
That is actually .001" LARGER than an Ackley Improved dimension. It is within .001" of most 9.3x62 ctgs. even though some books say .451" for the 9.3x62.
My Mauser and a Styer both measure .454" at the shoulder on a fired ctg., thus with .001" contraction after firing, the chamber has a .455" dimension.