Update by remedy Omg
Choose the map lockdown to get the cold as ice achievement as well. The coils should be on the centre platform.
Pretty simple to do.
-Can be done in custom game with a second controller or a friend.
-Simply turn shields off and start a game on stonetown.
-Run to the middle of the map in between the spinning circular thing and the base. You should see mutiple groups of fusion coils.
-the fusion coils are the barrel like objects that explode when shot.
-Have one person stand right beside the coils and the other one shoot them, and voila achievement. Then swap jobs and you both get the achievement.
Here is a link to an image of a fusion coil if you are unsure of what they look like.http://img3.wikia.nocookie.net/__cb20130624203642/halo/image...
In online just wait for a prime opportunity. some coils are in very common places only thing is can be quite difficult to make sure that someone is close enough.