Sniper Ghost Warrior

There are multiple places to get this achievement. You have to kill two enemies with one shot. This is only possible with a sniper. This is (offcourse) not going to work with a knive, grenate or pistol.

Look at the video below if you have trouble with this achievement.

This is really easy even though it may not seem like it. Simply find two talking enemies and aim so that the bullet will go somewhere in the upper body of the enemy at the back after exiting the first enemy.

i found the best place to do this was on then "NO MAN LEFT BEHIND" level. after you have made your way just past the wooden bridge with the jeep on the left hand side, go to the right side of the jeep and peak over the rocks. snipe the soldier and make your way to where he was stood. look to the right near the water and a soldier will be giving 3 others a bollocking. if u line yourself up u should be able to take out the one in charge and one stood behind him with 1 bullet. it took me a couple of attempts to get them lined up, and of cause as soon as they are hit , the alarms sound, so be carefull. good luck

heres a video showing the perfect spot very early in the game to get this achievement. it is about 1 minute in to the first level after training "one shot, one kill". enjoy

A good place to get this is the beginning of Chapter 7, On Your Own.

At the beginning of the chapter, follow the road, and you'll eventually come to two enemies on a platform off to the left. Kill them. Keep following the road, and as it turns into a downward slope, move to the far right side, and go into prone. Keep moving down the road, making sure to stay in the grass. A bit to your left you'll see one enemy standing still and looking at the ocean. There will be a patrol of 3 more enemies headed your way (Or they may already be there). When the patrol stops, there will be a line of 3 enemies. Position yourself so you can hit the 2 enemies' heads in the back (Of the line) with one shot.

It's really not hard to do, but it is buggy (Which is why I added the flag). I pulled it off about 5 times without getting the achievement before I gave up. Hope it doesn't glitch on you.

If you're gonna downvote, I'd appreciate it if you took a second and told me why. Thanks!

Another good location for this (in case you haven't gotten it before) is right at the beginning of Act III (Chapter 9). Right at the start of the level, walk a little bit and the game will instruct you to kill the enemies at the end of a long bridge. They will be lined up just for you. It takes 10 seconds after starting the Chapter.

Here's how to solve the glitch with the achievement not popping:

1. Make sure you have the rest of the single player achievements.
2. Erase the save file.
3. Move your profile to a USB stick.
4. Log in to your profile.
5. Make sure your Xbox is not connected to the Internet.
6. Start up the game and before you start up "Single Player", pull out the USB stick.
7. Start up Single Player but don't choose a storage device. Choose "continue without saving" and choose chapter "On your own".
8. Move down the road and take out the enemies.
9. Further down the road there are 3 soldiers approaching.
10. Hide in a fitting spot to line up two of them.
11. Pause the game.
12. Insert your memory stick and press the Xbox button, making sure your profile is logged in.
13. "Take the shot, kid!"
14. After killing both soldiers with one shot the achievement should pop. You won't get a time stamp but you will have beaten the Glitch Gremlin.

I hope this helps. It worked for me!