[joshcisn]

Lol. I just did it on causual. Get the torch bow (the crossbow as ReaperMojo said). Aim shot him to knock off the Krill (the bird things). Once they leave him open up all you can on him. I used the bow a few times. By the time he gets close to you, you can switch to your machine gun and do blind shooting to finish him off as you'll need to stay behind the cover.

I found using the bow/machine gun combo was much easier. The sniper rifle sucked.

Edit: If your like me and didn't have the bow the first time you got to the Raam checkpoint. You'll have to re-play the act 5 checkpoint (the start of the train) and grab the bows when you see them.