ID Mauser barrel

[Mika]

Has anyone seen a Mauser barrel like this? I have a couple of Swedish 6.5x55 rifles, one a 1915 Carl Gustav all matching and a sporterized one I had built from parts years ago so I am familiar, sort of. I got this “new” barrel years ago from a guy selling a bunch of mixed Mauser parts. He believes it’s a 6.5x55, the profile is military, the markings are a Swedish crown, the letters C.O. Near the threaded end, the number 6(9?) and overall it is about 25 inches, unfinished (in the white). I do not have a nearby gunsmith anymore so any clues here would help. Thanks!