What mesh should the glass for primers go through?
I'm going to say easily 100, 200, or even higher. For the glass to perform it's function as a frictionator - it must be very small. Regardless - the small pistol primer cup doesn't have room for anything large (a flake of anything will appear to be the size of a boulder). But the glass in particular must be the consistency of flour because it is so hard. A large particle of glass trapped between the projectile and the lans (the surface) of the barrel will make micro scratches - but if it's the consistency of flour - it will act more like a polishing agent.