Hello all. New member of course to asdk such a question (questions) I just bought a used AR. XM15 E2S bushmaster lower, and a S&W upper. On the lft side of the lower it says DFI Windham, ME. USA. The only markings on the upper is S&W on the top rail and barrel is stamped 5.65 NATO 1/9. The stock has the S&W logo. No other markings except serial # and the snake with upper and lower fangs. What have I got,,,quality wise? Why would the upper be changed out? Why is there no serial # on barrel? How old is it? Any information or discussion is appreciated. I realize this is not a choice, top tier tool, but I'd would like to know more about it. I carried a m4 bushmaster in Baghdad so not totally lost here. Thanks.