Well, I can't claim this as an original idea, I read it here somewhere a few days ago. My old Lyman 311041 had some rust in the cavities ( I know, I know, spank me.......) and when I read that I thought "Hmmmm, can't hurt!" I used some white vinegar and a clean toothbrush, that vinegar started bubbling as soon as it hit the metal! I scrubbed it for maybe one minute then rinsed with hot water. OMG! Coulda' knocked me over with a feather! It looked as good as new! I showed it to my wife, She said "I could have told you that would have worked, I use vinegar for cleaning lots of stuff!"