ORIGINAL: eldeguello
Actually, despite the fact that the ".30/'06" was first chambered in the M1903 Springfield rifle, it is not actually named ".30/'06 Springfield".
The .30-03 retained the 220-grain round-nosed bullet of its predecessor at a time when most world powers had realized the advantages of a pointed or "spitzer" bullet. In early 1906, a pointed bullet was mounted on a .30-03 case that had the neck reduced by a tenth of an inch to accommodate the reduced bearing surface on this new bullet. Thus, on October 15, 1906, with little fanfare, was born the .30 Cal. Model of 1906 - the ".30-06".
From top: .30 Ball Model of 1901 - ".30-01" or "Thick-Rim"
.30 Model of 1903 - ".30-03"
.30 Model of 1906 - ".30-06"