The videos below, courtesy of 'RyliesGames', show the basic route through this mission.
You'll start by quickly running forward and grabbing the M60, then use a light tapping method on the heads of the Infected for easy kills. If you're going for the
now (easy even on Hard difficulty with this method) do not reload. You'll get more than 15 by the time you exhaust your clip.
When you get blocked in at 4:41 of the video you'll be attacked by Infected from the opposite side and VC from where you came in. Contrary to the video move over to the left behind the broken rubble to avoid the fire from the VC and gun down the Infected with short bursts when they get close. Move on when the passage blows up and proceed through the rest of the mission with the same method.