Crud Buster is used to help remove dirt particles from difficult to reach areas without disassembling the firearm. Crud Buster is a powerful aerosol spray that helps “blast away” dirt and crud. Gun Degreaser is used to clean and degrease metal especially before bluing. Gun Degreaser is a liquid that comes in a bottle. Gun Treatment or Synthetic CLP Gun Oil should be applied after Crud Buster or Gun Degreaser.