The answer 2 people have already posted - 1 said lemon juice and the other citric acid for cleaning the brass = same thing. Citric acid with a drop or two of fairy liquid [NOT a squirt] will work wonders if simply swilled around in the washing up bowl. If then put individually in a shell holder on a (n electric spindle] and cleaned with paper tissue will both clean and polish the brass inside and out. Cleanliness IS next to Godliness in reloading and the absence of contaminants. You will be surprised how much dirt comes out on the tissue from the inside of the case especially if electrically spun and the tissue goes into a twisted worm inside the case.