A fantastic movie, but ...

Rating: 8/10 (12 June 2013)

The movie is fascinating in showing the real battle scenes, and describing the conflicts faced with a lot of GIs for the moral of the war.
Yet, I have a question here. The movie seems to be centered with two Sergeants, Barnes and Elias, the former was a killing machine while the latter tried to keep himself abreast of the chaos of war and stick to his own conscience and moral values. Elias didn't like Barnes, but he still regarded him as a reliable fellow grunt in battles. However, after the conflict in the small village, Barnes vowed to kill Elias and exactly did so on purpose when chance permitted.
My question is, is this teammate-killing a common sight in Vietnam? It is said the movie was partly based on the personal experience of Oliver Stone. But I am not sure whether this center-piece of the movie was based on real happenings or not.
It is interesting to note that there is also a similar parallel in the novel which FMJ is based on. In the novel (The Short-Timers by Gustav Hasvord), Animal Mother fragged down his own platoon leader intentionally.
Still, I doubt this was a common thing in the soldiers who served in Vietnam. It is just inconceivable for me that soldiers would kill each other for some disagreements, even it is about moral values.