The "spider webbing" in the finish is pretty normal for nickel guns that have been handled over the years. It comes from contact with holsters, dirty wipe rags, etc.
Below is my nickel pre-15 when I first got it. It had quite a bit of it.
With some careful polishing with Maas and a clean soft rag it now looks like this.
Some people recommend Mother's mag wheel polish, but I prefer something less aggressive like Maas or Flitz. Takes longer but feel it works better. It has taken some time, and I still pull it out occasionally and polish on it some more.