MAG-Propulsion barrel.

The Magnetic-propulsion barrel is an upgrade for the marksman in co-op. It increases the range and increases the amout of damage dealt by a headshot. It costs 200 Grey tech and is availible at level 16

Trivia
The way the MAG-proplusion system works is by using an internal copper coil (through which electricity is passed) to create a magnetic field thats stablises and accelerates the bullet as it travels down the barrel.