You probably have a military Mauser made by FN sometime between WWI and WWII.
After WWI, the German Mauser company's business was pretty well taken by the Belgians.
The FN company made Model 98 Mauser rifles for the world, including just about every country in South America.
Most of these rifles were large ring M98 Mauser's, with slight alterations for each buyer.
Most of these were variations on the FN Model 1924/30 and the 1935 models.
Sounds like your rifle has had the bolt and action bright polished. Take care to keep a coat of lube on it or it'll rust quickly, since it's just bare steel.
TO positively ID the exact model and what country it was made for, look for a stamp on the left side of the receiver, between the barrel and the rear of the bolt.
If you can remove the scope mount, you can describe the crest which was specific to each country.
These rifles were fine quality, and make excellent shooters and custom rifles as long as the action is in good shape.