Most of the dental labs that I have worked at used 4 different medias. Walnut shell, kiddie play sand, 50 micron aluminum oxide & glass bead (I dunno what mesh, very fine). In my own lab, I only use the 50 micron aluminum oxide. I've done a couple of beater revolvers & they came out looking surprisingly good with cold blue. I'd like to try the glass beads, but I have no use for it in the lab & it would contaminate $1,000 castings that I use aluminum oxide to clean.
I use a pretty expensive dental abrasive blaster that consists of a pencil-type wand with a carbide blasting tip that is hooked by lightweight hose to a 2 pint "hopper/mixer". In the dental industry, it is used to blast casting investment and/or carbon from very small castings with the tip anywhere from 1/4" to 1" away from the surface being blasted. For my artwork (I use it to etch intricate patterns on glass) I hold it anywhere from 2"-4" away from the surface in order to get a consistent look/texture in the finished product. On glass or metal, it is important to do the entire job from ONE angle, kinda like an ink jet cartridge travels back & forth over the paper it is printing on.
A couple of notes- Aluminum oxide is a pretty aggressive abrasive, if you stall for a second it will eat right into a surface (I use 15-20 pounds pressure for light work, 25-35 pounds for medium work & up to 50-60 pounds for heavy work- all coming out of about a 1/2mm to 1mm hole). It leaves a sharp surface, much like very fine sandpaper. Glass beads kind of "peen" the metal, leaving a pearly feel (they can remove metal, but much more slowly then aluminum oxide). With any abrasive, it is better to go over the surface several times from a greater distance & with less pressure then to overdo it with too much pressure too close to the nozzle
When Banjos are outlawed, only Outlaws will have Banjos
The Bible is my lawbook. I turn the other cheek when applicable, and spend the rest of my days resisting evil at every front, until I have breathed my last breath.