Kill Macgruder. Easiest way to do this is to pull out your dynamite bow
and shoot it at the ground where hes gonna walk. Then when he jumps on a 
large ledge shoot him in the head with your rifle and shoot the large
dynamite pack in the air that he throws. Three times and your done.
-Richy.

McGruder has a certain routine the way he fights in the 2nd part of the
battle. 

He will shoot at you till you shoot him in the head then he will throw
a large dynamite pack then 3  little dynamite sticks. It is the same 
routine everytime no matter how the battle starts.