It's called the TR-116. It fire's bullets made of tritanium, which is a metal that is many times harder than diamond. When the gunman is wearing an Exographic Targeting Sensor (which looks pretty much like a knockoff of the DBZ "Scouter" units) which allows him/her to see through walls, and also the end of the gun barrel is equipped with a Micro Transporter which allows bullets after being fired from the gun to be teleported to any selected location, this gun is the ultimate sniper weapon. When this gun is used in this way it allows anyone to get ridiculously cheap kills on anyone.
Below is a picture of Esri Dax holding this weapon and wearing the Exographic Targeting Sensor.