The neck length of the '06 is .007" shorter than the 30-03, The OAL case length is shorter also. When the 1903 was recalled from service, the barrels were replaced if neccesary due to excessive heat caused by high amounts of nitroglycerine in the powder which gave a barrel life of between 700 and 1000 rounds. Barrels that were found to be in good condition were shortened and rechambered to the new,shorter 30'06 and loaded with 150gr bullets. The leade in the throat was changed also.
