how does expansion ratio fall into all of this. You know the ratio of case capacity to bore diameter.

I have no idea on the accuracy of the statement, but someone once told me that the 222 rem, 308 win, and 458 win mag all had similar ratios.
Don't holdme to the truth in that, I don't know.

There is something to be said about larger diameter bullets being more accurate due to flaws of the same size having less of an effect on the overall performance due to less of a percentage of overall size.