If I may offer my opinion: just brush the gunmetal on. Don't waste your time trying to imitate an effect when that effect is a by-product of the basic process. So many times over the years I've seen people try and dry brush or whatever their way around and it never looks like the real thing. The brushed look is just the way the light catches the peaks and valleys of the brush strokes, variable paint thickness, and variations in mixture. Why waste time trying to fake it? You can do it no problem :thumbsup
Cheers,
Dave