The color of the barrels after etching CAN be manipulated by the browning solution and also the alloys in the metals. Steel with a manganese content (10XX Carbon Steel) will typically etch black. Nickel will produce silver, and chromium gray. And from the limited composition analysis study it appears at least by the 1890s quality steel barrels were at least 1020 advancing to 1030 & 1040 Carbon steel, sometimes rephosphorized.

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