Took out both Hunters using only the Sticky Detonator in mission 7.
If you're going to start Once you've reached the part where there are two Hunters inside the lab, grab a Sticky Detonator from inside the white room or from the left corner of the room. If you're replaying the mission to get this achievement, you can find a Sticky Detonator as soon as you reach the first door. The hunters can be killed with two shots on easy mode. This video is from our unofficial game guide. You can view the full guide here