I was taught, many years ago, that sand blasting will actually make the part "bigger." i.e. Your pin hole clearance would get smaller. The media effectively peens the surface leaving small raised ridges. If you mic'ed a piston before and after blasting, it would be a thou or two larger after blasting.
Now if you had real aggressive media, high pressure and aimed at one area for a long time, I'm sure you could wear away the surface as well.