This is considered one of the hardest achievements in the game. If you have a team of reliable players who have mics, your chances of getting this achievement increase dramatically. A good spot to use is the rooftop of the small shack on Dustbowl stage 2, capture point 1. There is a small section towards the back of the roof that sticks out to the side, place your gun here and alert your teammates if your gun is under fire. This gun stops people from leaving the trench from all exits so you can quickly rack up kills on unsuspecting enemies.