If you have access to a bead blaster, my suggestion would be to bead blast all of the visible metal. While there are many different types of synthetic gun coatings available in the USA, they are probably not available in Norway. So after you have bead blasted it, I'd say you might consider painting it black with can of aerosol flat black paint. If you do not have access to a bead blaster, use fine sandpaper to smooth the surface. At least in the USA, it is very easy to find inexpensive wooden grips to replace those heavily worn ones now on it. Maybe not so much in Norway unless you can buy from eBay.