GUNDAM OPERATION TROY

You can also get the following achievement as well as the Master Sniper(Single) one:
Solution for Sharpshooter(Single) In Mobile Suit Gundam Operation: Troy
I managed to get this achievement in the E.F.F. campaign on MISSION 04. You will spawn as the Sniper class.

This mission has enough enemies on to get this achievement easily. Simply aim down the sights (click in the Right Analogue Stick twice) and start shooting away.

Remember to run back to the Health and Ammo crates if you are low on supplies or need healing.

Please comment if you vote negatively. I will edit my solution to make it better.

This can be done very easily on the 4th mission. You will start with a sniper rifle, and should get the achievement before approaching the tank. Just take your shots from a distance or stay close to a health box. You do not have to use just the sniper rifle, all weapons will count towards this....

But you might as well go for the sharpshooter achievement in the process as well.....good luck