Marc,
I do plan to leave the metal bright and let it age naturally. I really like the contrast against the darkly stained maple. Incidentally, stocks are stained with ferrous nitrate (AF). Mine has one coat of leaded linseed oil followed by a few coats of BLO, then a few coats of Bio-Poly. Pop's is just Bio-Poly.
We had bought a couple gallons of the BioPoly for finishing walls and floors in my old house. It is a linseed oil based finish. Not sure what all is in it. I know it uses a citrus based thinner and has some hardening agents - most likely rosin. In any case, rubs on just like any other linseed oil based finish. Figure if it works on heart pine floors, should work on rifle stock. I don't tramp across the gun in my work boots. So far, so good.
Paul