Very good post, Cosmoline.
GEM, I think the term "battle rifle" tends towards a rifle that is intended to fire one round at the target at a time. Even though it is capable of full-auto, the M-14 is a "battle rifle" because it's generally used in semi-automatic. I don't think the M-16 or M-4 are a battle rifle, because I attribute that term to a medium-power weapon, not a light weapon like these. I would consider them to be "assault rifles". The AR-15 doesn't really fit either category - it fires a light cartridge, and it isn't fully automatic.
Of course, this dichotomy is one I use in gaming, not really in real life.