Ammonia will work if you let it sit in there for at least 30 minutes. Most copper eliminators use ammonia with other ingredients. Wait 30 minutes. Pass another wet patch. If it comes out blue soak some on a brush. Pass it through a few times. Follow with a couple of clean wet patches. Let it soak for a few minutes then repeat. If all else fails then some J&B Bore Bright, or Bore Paste will be needed. Just remember if using them, a little does a whole lot.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.