I am new to the AR-15. I have wanted one for a long time now. I have a question, what is the breaking in time for a AR15? I am getting one that has a 120 rounds down the tube. I have been told that there is a round count per cleaning time. When I go to the range and shoot, when I am done I clean my guns. Do I need to clean between shooting at the range? I thank you for your time in this matter.