I sometimes use Birchwood-Casey chemical case cleaner, which is a solution of phosporic acid. It has worked well for me, but I have to mix it a little stronger than the instructions call for to make it effective for really dirty cases. I have been using it for 15 years or so and haven't had any problems with any cases that have been cleaned with it. With rifle cases, I usually decap the primers (using a universal decapping die) so they will dry out faster. Be sure to properly rinse your cases. I give mine three rinses.