When I hit the range yesterday, I hit the motherlode, picking up over 600 .223/5.56 casings. Some were fresh, some were only slightly tarnished. Since they had been in the snow/ice/water, I put them in the oven at 200 degrees for 30 minutes to dry them out. I used the wife's bacon pan so they would stand up, allowing the water to evaporate out through the neck. Tonight, I was sorting by headstamp/caliber marking, as most of it was LC brass. About a dozen had a light green "corrosion" inside the neck, but not the casing itself. The date stamp appeared to be 75 or 76. The newer dated casings were all clean inside the neck. I was able to get the "corrosion" out with a few passes of a .223 bore brush. It reminded me of some of the Yugo M67 casings I've found left at the range after a few rain showers.