In 1900 Senior Military Officers were the people who made these decisions. They were still concerned with the traditional threat of massed horse Cavalry charges on the Infantry. They assumed the need for a cartridge sufficient to drop horses. Apparently they viewed the 7mm Mauser insufficient. But they scaled it up from a 0.284 calibre bullet to a 0.308. With a 220 grain bullet compared to the Mauser's 175 grain. The cartridge case was scaled from the Mauser's 57mm to the .30/03's 63mm.
When the standard changer from the .30/03 too the .30/06 the case was shorted one millimeter.
