I read an article a couple years ago in Field and Stream, I think, where they were comparing rifling wear in different calibers. I think it said that the 30-06 and the 30-30 were the easiest on rifling, can't remember why. I'll have to see if I can find that article again because I was really surprised at how fast the rifling wears out on many common rifle calibers.
In the Sierra reloading manual they describe barrel life in terms of pounds powder burned instead of the number of projectiles fired.