I have RWS 34 and soon after I had fired about 100 - 200 shots through it I noticed that the bluing was gone from in back of the front sight on top of the barrel .
What I found was , that when I was cocking the gun , I was holding it under my right arm and slapping the front of the barrel to get it open and then grasping it with my left hand and pulling / cocking it back .
What was wearing the bluing off was my WEDDING RING !!!!
I have used a Presto Gun Blue Touch Up Pen and works well to cover up minor scratches. The pen contains an acid that oxidizes the metal making it "blue"