[lcmunn]

The leaf style rear sight (rather than tangent type) suggests that the rifle is probably still in its original 7x57 caliber. If the bore condition is good or better, this may be a decent shooter but you do need to get the caliber question figured out and it would be good to have the headspace checked before you shoot it. A lot of collectors bristle up and nash their teeth over a sporterized military rifle, but the practice has been going on for a long time and a lot of today's old timers got started shooting "high-powered" rifles with a cut down military rifle. The 1893 style Mauser action saw a lot of war use and served well.

 

[lcmunn]

What version of "fits fine" are you looking at?

I just tried a 6.5x55 round in my Ruger No. 3 (7x57) and it fit up to the top of the extraction groove. The block would not close. In a 1908 Brazilian, the round chambered but the bolt would not even start to close (I did not try to force it). A chamber cast as per Retread's suggestion would be very wise. At the least try a 7x57 round for fit before firing anything. It may also "fit fine". Your rifle's sight hinges at the rear like a Spanish 1893 long rifle sight. The Swedish 1896 rifle sights hinged to the front. Replacing the barrel, resetting the original sights and re-stamping a Spanish style serial number seems like a lot of work for someone to have gone to when these sporters sold for $12.95 back in the early '60's. But you never know???