Precisely.
And that explanation sucks. Even that grain of sand has to come from somewhere, and you can fire off thousands during a mission easily.
Take a handful of fine sand.
That's a thousand grains easily. Probably more. The gun has plenty of room for many handfuls worth of tungsten sand or something else with a high melting point.
Secondly, a grain of "sand" fired at railgun-like speeds would be rather innefective. It would burn up from friction in an instant, or would really cause such pitiful damage it would be unnoticable. A microscopic wound would heal in a minute - what you describe is LESS than being pricked by a needle (ok, more like, a super-small needle going trough you, but with a opening that small, you wouldn't even need a band-aid)
Over the ranges involved the projectile will still be effective. If we were firing twenty kilometers or something you might have a point, but we're not, are we? Engagement range even for sniper rifles is usually under 500 meters.
See, the problem with this concept is the Tunguska lesson. A low-mass very-high-velocity object hitting a many times more massive object at rest will transfer its velocity explosively. Similarly due to the behavior of living tissue your exit wounds will be considerably larger than your entry wounds, the higher the velocity, the larger the exit wound. The wonder is not that these do damage, but that if you hit them in the torso a single shot doesn't cause their whole back to explode outwards.
At least the roleplaying and story is as good as ever. Better, if anything. The new characters have a lot of personality and the dialogue seems sharper. I like it.
I haven't gotten too much out of the personality of the new folks yet, honestly, but I'll say that I'm pleased by the dialogue. The whole reaction of "Now with more F-bombs!" was bogus. The addition of swearing makes them feel a bit more...human, like they're actually reacting to stress. Shepard's dialogue is a bit tighter over all.