How about something permanent that doesn't require specialized tools (like bead blasting equip)? I was thinking about sandpaper. Just not sure what kind and grit.
Buy a couple sheets each of 800, 1000, and 1200 grit wet-dry sand paper made by 3M, I pick mine up at auto parts stores since most regular hardware stores don't carry it. This sandpaper is very fine and is good for dulling down surfaces to give a satin type but not shiny appearance, without leaving deep scratches in the metal in case you want to polish it out. It comes out looking like a brushed finish without any streaks, so I think it comes out more uniform looking. Tape around the section of the top strap you want to dull down on the revolver and give yourself an even bracket that will get sanded, this ensures your work looks uniform and that any areas below the top strap don't get sanded. Make sure to use a bit of gun oil with the wet-dry when working the metal, it makes a world of a difference in the outcome. Experiment with the 800, 1000, and 1200 starting with the lowest first, and see which results you think look the best. Anything you sand that you don't like the outcome on can be polished out with Mothers Mag Polish pretty easily by hand.