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Sorry I meant spanish mauser.

Sounds like it's an enfield of some sort. That being the case lots of light coats of raw linseed oil
Thin it right down and do multiple coats.

For sporting arms you can't beat true oil

If you really want to restore it without destroying it's value (ie by sanding) then the correct and most unobtrusive method is to use calcium "carbonate" (chalk powder and not calcium bicarbonate as...