That's something I'll have to try with brass parts. When the brass black is used full strength, it builds an oxide layer quickly, but it tends to be soft and flake off sometimes.Sorry, Kurt for highjacking your thread...
Yes, the barrels are CNC-turned brass. I use 'Brass Black' diluted with water 1\10 (one part Brass black, and 10 amounts of water), then I hold the barrels in the bath for 20-30 minutes, brushing the surface (both sides) occasionally. This is a slow blackening process, but it resists light scratches. The surface must be spotless from dirt\greese, A MUST!