Shiny brass -- it may not shoot more accurately, but it does make you feel better about your hand-loaded ammo. While it's not necessary to get brass bright and shiny after every firing, it is a good idea to clean powder residue, grime, and grit off your brass before you run cases into sizing dies. There are many ways to clean cartridge cases.
What's The Best Way To Clean Brass?
Ultrasonic Cleaning: What Is It? How Does It Work? Types Of
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UltraSonic Case Cleaning
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Ultrasonic Cleaning - FasterCapital