Kill 30 Helghast soldiers in under a minute

This is best done on Easy difficulty while playing as Rico on Chapter 4, Strange Company. You will have to go down a set of stairs as opposed to sneaking around while playing as Templar or Luger, and kill plenty of enemies along the way. A few tips to expedite and ease up your progression are listed below:

Rico's Chain gun doesn't need reloading (except for the secondary fire), but that doesn't mean you can hold the fire button forever. There is a cooldown timer that keeps your trigger happy finger in check.

Tap instead of holding the fire button. That way, you will never have to worry about overheating the heavy machine gun.
Be quick on your feet.

Aim for the head. There are a few Elites along the way, so all headshots count.

You get three secondary fire rounds. Save them for the larger groups, and only fire them when you're sure you will kill everybody on the floor with it. This is to prevent you from going into the reload animation while there are still enemies around.

That being said, you will probably get this trophy without too much trouble. If for some reason you don't, reload from the last checkpoint and try again. All in all, there are 40 enemies during the staircase fray.