After trying for hours, then searching on TA for a Guide, Youtube and others boards … no Guide EVERYWHERE.
So after more trying and dying, i finally found a good spot, but its still not easy to get. A great spot to do this is on the mission Insurgent Stronghold. Play until you arrive at the last tunnel. The enemies in the area will move around a bit, so this may require a little trial and error. If you fail, restart the last checkpoint and try again.
If (1) is moving behind the house – restart. If (3) move inside the house – restart. If they stay still until (2) move away, move with (A) to Point (7). If (1), (2) and (3) are ready to execute (marked red), move to (8) – press Execute, then kill (9). At the same point mark (4), (5) and (6). Make sure you kill them with your Weapon, not with a melee Attack (Meleekills take to long).
– SC-IS Pistol: Red Dot Sight, Laser Sight, Match Grade Ammo, Weigt Balance & Accurized Barrel
– SC4000: ACOG Sight, Laser Sight, Extended Mag, Match Grade Ammo, Weigt Balance, Tuned Recoil Buffer & Accurized Barrel
– Googles: Intergrated Optics (Blue)