Glass beads make a burnished finish similar to some stainless factory rifles. 70 grit aluminum oxide media is more aggresive and makes a dull, fairly smooth finish. Silica sand (sugar sand) is more aggresive when fresh and makes a dull, fairly coarse finish that gets darker in a few months. For a nice uniform finish you have to remove all machine and turning marks first.
Hope this helps, Tom
Texas State Rifle Association Life Member
NRA Endowment Life Member
A big fast bullet will beat a little fast bullet every time