This picture isn't very good, but I wanted to show the brownish metal color as best I could, its under fairly bright light. In the normal light it looks a bluish plum color. The one picture above of the cylinder shows it best I guess. I don't know why the color changes like it does. Lighting I suppose.
I guess not getting that far in the weeds with these things comes from my 6 years as a Senior Instructor at the US Army Ordnance School in APG MD. where I taught 45 bravo small arms repair and 45K artillery repair. We only went so far with trainees and taught them when it need to go GS or Depot level maintenance.