Whenever I use a suppressor on my .300 BO on either one of my builds, I get a Copper/Brass looking residue in the upper and lower receiver. A buddy of mine that has more experience than me, but no military background says that it's unburnt powder due to the suppressor. Weird, as I also load my own rounds. This looks like copper or brass shavings. Not powder. Although, I could be wrong as I am a suppressor noob. I have 4 suppressors, and my 6.5 Creed doesn't do this, but it's a bolt gun. Nor does my handgun suppressor. Pics coming. Is it unburnt powder? Or something else? I need to know as I am a former Marine, and weapons maintenance is paramount with all of my weapon systems.