This can most easily be done in the Main Mission "The Deserter
" in the Montuyoc
You will also need to have the following skills:
- Flare Gun
- Explosion Radius Epic Skill (Recommended)
As you approach the group of 7 enemies (including the yellow target), hide behind the truck in the field. Now, shoot a flare in the center in order to have the enemies move towards it. Once they start coming together, run forward, equip your C4, throw into the middle of the area and explode it. If you kill everyone, the achievement will unlock.