Looking closer at my WWI bullets, they have a groove for crimping the case. In front of the groove towards the tip, the diameter is 8.26 to 8.3mm (0.326), but in the back (i.e within the case)the diameter is only 8.15 (0.321). This probably means that a 8.3mm cylindrical bullet might not chamber.The bullets are ogival both ways, and do not have a flat bearing surface. Pictures are on the way.
Of course those are the D bullets, and the M bullet might have been quite different.
Best regards,
WC-