M15A2 by all means at least lubricate the M15A2, I presume this is what you are shooting. By not lubricating you will get premature wear in certain areas. By not cleaning you really can't damage your weapon. By not lubricating properly you can accelerate the wear. I have a M15A2 that I don't always clean after leaving the range. Sometimes I go two trips to the range without cleaning, but I always lubricate. I was even a Grunt, but I learned that you can over clean when it comes to the tools and techniques used to clean ARs. I have seen people taking rifles into hot showers, use shaving cream, breakcleaner, and probably the worst tool I have seen and used while in the Army is a piece of clothes hanger to get into hard to reach places.
The horror
The horror
No Slack!