Dart Gun Sniper Rifle

So, I've had this idea for a weapon for awhile, pretty much, it's a sniper rifle that shoots darts that blur the targets vision, making it harder to see, and/or slowing them down as well, sounds good?

the plasma flechette rifle?

Plasma Flechette Rifle is more of a lock on and fire automatic weapon kind of gun, the one I'm thinking about is more like the Rosemary, Bolt action, single shot.