Seems to me the Ruger base is .532" - same as the belt diameter of normal belted cases.

Since the normal belted 2 1/2" case has around 85 to 87gr. capacity, I would assume the fatter Ruger case has about identical capacity as the long .416Rem, that is, as long as the Remington case has the larger shoulder diameter of the 8mm Rem. mag.(at least larger than the .375 H&H)

This coul.d pretty much even up the 6gr. advantage the shorter Ruger case has over the longer H&H case to start with.

A straight 2 1/2" belted case, the .458 Win Mag has about 92gr. capacity. Different makes of brass will vary, of course.

The will all give roughly the same ballistics, so it's simply a case of semantics and parts availability, or personal choice.