I have some 300 PRC brass that I threw in the tumbler to clean up. I am using a Frankford arsenal Quik-N-EZ tumbler with crushed Walnut media. I also threw in some 22-250 and 270 brass with it. The 22-250 and 270 brass came out clean and 300 PRC brass came covered in gunk. I pulled it out and cleaned it off and threw it back into the same media and it came out clean. Curious to what is causing this and how do I avoid it without changing up my setup. Pictures are after the 1st tumble and after they were cleaned and thrown back in.