Brass marks at ejection port

[mitchell6776]

I know it's very common, but does anyone have any tricks for removing brass marks at the ejection port on a blued BAR?

[Black River Militaria CII]

I have used fine brass or stainless wool with a good lube and lightly go over the brass stains. Regular 0000 steel wool works as well but for bright blued finishes better to use the softer metals. I use brass punches and hammers for a lot of work and usually any brass stains comes off by rubbing with papee towel, or coarse cloth and some lube. Hope this helps.