I haven't a clue why its happening. CCI caps shouldn't corrode. What I seen was a fair amount of rust covering the inside of the hammer cup. I know now what its from!!! I just now figured it out.
I store my rifles in a standing upright position with its hammer down on its nipple. If there were any water after barrel cleaning left in its firing channel I bet it migrates out its nipple over time. That way no matter what I put on the hammer after cleaning wouldn't hold up. (CLP or whatever) What do you think arcticap possible or not?