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.
idahoguy101. Thanks for that post. I knew the 30-03 was a scaled up 7x57 and the 03 action was "copied" from the 98,(actually it was more the magazine configuration patents that were infringed from my understanding) after the outing to Cuba's San Juan Hill, but hadn't seen that reason before. I had understood that part of the reason was that the 30-40 had only been in production for a few years and there was all the tooling for the 30 cal barrels, with the 220gn bullet being a carry-over from the Krag as well.
