It is not possible to kill Magruder by shooting him, as he is wearing armored 
plating. Instead, use the bow with exploding arrows. Get Magruder to chase you. 
As you are backing away from him, shoot an arrow at a geyser as he walks over 
it. The flammable gas coming from the geyser will explode and damage Magruder 
until he is almost dead. Then, when he is on the higher level, shoot him in the 
face with the rifle until he yells, then get into Quickdraw mode. Get ready to 
shoot the big package of dynamite when he throws it. After shooting a few sticks 
of dynamite, the roof will collapse on him.