Sure looks like the original barrel and even if it's 7mm I'd still wanna make double sure the chamber is still 7x57 . On some of these old military guns that have been sporterized there's no telling what else has been done to it. A Cerrosafe chamber cast or a good gunsmith could solve that mystery. Probably still 7x57 and that would be a neat rifle but always be sure of it before proceeding. If it's a 7x57 and you get to shoot it do we get a range report? Oh, and how's the bore condition?
Sure looks like a model 1912 Chilean Mauser to me also. That one's been cut down some and who knows what it's chambered in now. They were all originally in 7mm Mauser ( 7 x 57 ) IIRC. I seem to recall those having straight bolt handles but there may have been some other variations or that one got bent down when the rifle got cut down. Looks interesting, though, and I second the motion on the Cerrosafe.
The Chileans did have some carbines in large ring but made by Mauser itself rather than Steyr. It is possible that the Chilean military or someone else put a 7mm carbine barrel on it. If I recall correctly, Brazil had some 7mm carbines in large ring as well and you can still see those carbine barrels for sale every now and then.well, the front sight still looks military, so perhaps it was a carbine?