Here's the response I got from Lee

Benny:

That is correct, we do not recommend cleaning the brass before resizing it. The dirt and soot act as a lubricant when sizing the cases so will make it easier to size. Also, clean brass tends to gall or leave deposits behind on the carbide, which will build up and scratch your cases. While the scratching and scoring doesn't look pretty, it will not effect how your reloads perform at all.


Thank You,

Laine
Customer Service