Jack,
I am no expert in these things but Terry Wieland in his new book Dangerous -Game Rifles states on page 164 that "the .470/.465/.476 are all based on the .500 case with the same base dimensions." I assume he is correct but have no independent knowledge. My point refers to the fact that to make a bottle neck case they first stamp a tube of the widest dimension of the case. Then it takes another step to neck that case down the the bullet diameter. If they are stamping out .500 dimensioned cases to neck down to .470 I assume they will continue to offer the .500 since it is an earlier step in the process.