Today I completed this achievement. I am in the last part of the game and reached the
Point of no return campsite. I backtracked to finish pending achievements and undiscovered stuff in previous areas and hit a dead end when trying to complete
Widowmaker because I couldn't find any enemies.
As reference, I am playing in Hard difficulty and I have 100% on all skills, weapons and upgrades. Save file reads 97% completion:
From reading other guides I decided to try
Shantytown, as other guides point there for enemy respawn points. Luckily I found one location and was able to pop the achievement!
SOLUTION: Fast travel to the
Helicopter Hill campsite in
Shantytown. Head straight over to the Tomb using the rooftops. Jump your way until you reach the last rooftop before the clearing in front of the Tomb (the one with a small crate that you can use for cover). In-game GPS coordinates read
53N 712576 UTM 3416081. A conversation from enemies can be heard at this point and if you aim toward the interior of the Church (the actual Tomb is below it) you should see 3 enemies praying:
Just shoot in their direction to get their attention and then head towards the top of the building right behind you to get better cover (you will need to double-jump on the board/wall behind you). You let them come to you and from your vantage point pick them off one by one as they climb over the rooftops to get to you. The sweet spot is in the top floor of that building. In-game GPS location reads
53N UTM 3416086:
IMPORTANT: Don't be stupid like me and kill
any of the enemies while they're
inside the Church. In one of the repeats I accidentally killed one enemy and the next spawns would only generate 2 enemies instead of the initial 3 I had on the previous tries.
Once you have killed the enemies, loot the corpses to refresh your ammo and head back over to the roof with the crate to start the secuence again until you have your achievement.
Unlike what I have read online, I did not have to kill all 40 enemies in one go. It seems that my count from previous shotgun kills did not reset even after dying and reloading checkpoints multiple times during my play-through. Then when I decided to head on to
Shantytown to finish this achievement, I just killed a few enemies and the achievement popped. Not sure why other solutions mention that the kill counts resets between deaths or checkpoint reloads. Luckily for me, that was not my case!
ALTERNATIVE: There was another spawn point that is directly to the right of the sweet spot where you take cover from the Church enemies, on the top of the 2 level tower across from another clearing on the ground level. For reference, the tower is on the rightmost side of the area when looking towards the Tomb from the
Helicopter Hill campsite (and to the leftmost side when looking at the in-game map). However, only 2 guards spawn there. To activate the secuence you have to head to the bottom of the tower until you hear the guards speak. The in-game GPS location reads
53N UTM 3416090:
Same as with the Church method explained above, you shoot towards them (careful not to kill them while they're in their spawn point) to get their attention, and then look for cover while you let them come to you so you can kill them. Rinse and repeat.
Hope this helps anyone still looking to get this achievement. Cheers!