I remember watching a Vietnam film several years ago that followed soldiers through training. I can only remember one scene where the drill instructor teaches the recruits about the AK-47 and that it makes a distinct sound that they must remember so they can easily identify an enemy based on its sound.
I think there was an abandoned building in the background of the scene and I think someone was shooting out of a window (My memory of that is very fuzzy and it's possible that it will end up being from a different scene or even film but I think that is unlikely). I always believed that this film was Full Metal Jacket, however having watched it recently the scene was not there and I'm fairly certain it had different actors in it. I also believe that this film was well received.