I just measured a factory Kynoch 9mm Mauser round with 245gr. bullet.
The rim diameter was .464" and the base diameter was .4645".
Probably muddies the water somewhat.
Just checked my Pet Loads and did not find the 9x56MS.
Just checked JJDonnely's book which lists 9x56MS:
Rim dia...... .464"
Head dia.......464"
Shoulder dia. .408"
Case Length...2.22"
which is 56.388 mm