Quote Originally Posted by RustyShackle View Post
You could run the face over a 1000 grit sandpaper that is placed on a very flat surface. Use light circular motion. It won’t help true the action but it will square the face. You will likey find high spots.
Rusty's method is going to help in your case. It surely won't hurt. To me your photo of the thread end of the receiver shows high spots (shiny spots). These will interfere with the lug torque and may cause poi change during shot strings. You are looking for a good flat surface to mate with your new lug. With the 1000 grit paper it would take forever to booger it up. Personally I would start with something much coarser and finish up with the fine paper.
You most likely will see the edge that is not "blued" when you are finished. Options are cold blue or paint (no big whoop).