As originally issued the M 1903 service rifle fired the .30-03 cartridge which used a 220 gr roundnose bullet @ 2300 fps. In 1906 the cartridge was changed to the .30-06 which used a 150 gr spitzer bullet @ 2700 fps. To accomadate the shorter bearing length of the new bullet the neck of the case was shortened, to the best of my recollection all other case dimensions remained the same. The bullet seat (throat) in the chamber was also shortened. Most bbls of existing guns were shortened from the breech enough to allow re-cutting the chamber to the new dimensions. About the only rifles one is apt to find today chambered for the .30-03 would be one of the above mentioned Winchesters.
