Well.... actually in fact the longer length was not needed with a shorter bullet in the 30-03.....so 63 mm was determined to be sufficient length FOR the lighter bullet.
THEN the 30-06 was designed w/the 63mm length case IN 1906. It was MORE the bullet size/length that determined the length of the case THAN the space need for the powder
uh huh, ummm Well Apparently, "Shaman" was NOT there.