1. Have a friend or two join your squad.
2. Join a CONQUEST game on ATACAMA DESERT
3. The person going for the acheeve switch teams, you can do this by looking at the scoreboard and going to recently played with people and join session in progress of anyone on the other team.
4. Meet at flag "C" on the desert side there are 3 single level buildings and 3 two level buildings.
5. The person going for the acheeve should be assult class with a grenade launcher, this is the easiest and most controlled way.
5 1/2. Destroy the building, using the assult class drop an ammo resuply at your feet and start taking out the walls and corner with your grenade launcher and the building will drop
*Added for Shock*
6. once you get it then just change positions.
When I started with a friend it took about 25-30 minutes to get it and then another friend joined and it only took about 15-20 minutes with 3 of us . . . your can get about 5-6 kills per round with 1 person 10-12 with two.
Good Luck