pitting

Hi All, Pretty new to here, so apologies if this has been covered before, but my old stalking rifle is starting to pick up some black pitting on the bolt (see pictures). Is this normal? Is there anyway to clean it up? Any help gratefully appreciated! Tom

Earlier this week a friend helped me zero a brand new Tikka T3x in .308 Win. On the end of the barrel was a new DPT moderator. I fired 57 shots. I took the mod off, followed the manufacturer's instructions and cleaned it in warm soapy water. There is some slight pitting on each of the sections...