I looked at a 27-2. The bluing looked really good, but under a strong light there were brown streaks below the bluing. What would cause this?

I'm guessing you used a led or floressant type light to inspect the gun. I know I freak out whe I use my surefire to look at my 29 for the same reason. The reason there are brown streaks is that bluing is a controlled rusting process. Nothing wrong with it from your description. I suggest just using regular light to ease your worries.