The 30.06 was developed from the 8mm Mauser and this also produced the Springfield.
The Spanish–American War of 1898 the us found out the hard way that the 30.40 Kraig had its faults.
The Spanish had Mausers.
The case was longer because ........
Comprehensive tests were conducted in 1904, '05 and '06 which brought about our adoption of the M1906 bullet. This very closely resembled the German bullet of 1904, being 150 grains in weight, flat-based, pointed and having a cupronickel jacket over a lead core. When this new bullet was first tried in the Model 1903 rifle it posed a very interesting chambering problem. Since the ogive of the pointed bullet placed the full diameter 0.2-inch farther back than the old round-nosed type, the new projectile had a jump of this distance to touch the rifling. This factor permitted gas leakage around the point during this interval and caused erratic positioning in the bore, with the result that accuracy was poor. Correcting the difficulty by seating the bullet farther out in the case left a seating depth of only a sixteenth of an inch - far too little for field service. This also made the cartridge length exceed the permissible limits for use in the magazine. The solution to this problem was attained by cutting 0.2 inch off the rear end of the barrel and rechambering it with a reamer having a shorter leade. This in effect moved the rifling leade to the rear so that a bullet with adequate seating depth was properly aligned with the bore in close proximity to the rifling. With the increased seating depth, the long neck of the 1903 case overhung the bullet ogive, so 0.07 inch of the neck was trimmed, resulting in a revised case 2.49 inches in length and having a capacity of 4.35 cc. This combination gave good accuracy, and all 1903 rifles then in service were recalled and altered to the new specifications, although the rifle's designation of "Model 1903" was retained. The official designation of the new ammunition as noted on contemporary box labels was "Ball Cartridge, Model of 1906, For U.S. Magazine Rifle, Model of 1903".
excert taken from The Rifleman's Journal
So basicly it is a 8mm maiser case with a longer neck in 30 cal.
Trying to keep up with the Germans and it did a goo job.
Went on to become the 30 M1 Bal.
By the way a us court ruled that royalties were to be paid to Paul Mauser as the 30.06 and Springfield 1903 rifle were mauser copies.