First off this is my first AR and after doing a lot of research and saving some pennies I purchased my first part. I went with BCM 16" m4 upper just from all the great reviews from this site and others. It was one of the bigger purchases so I thought I would get it out of the way first. So I have a ways to go but had a question about rails, since it doesn't come with one. Is the rail I need a 9" middy or is it a 7" carbine? I may go low pro gas block and nice rail down the line, so then it might not matter, but will probably look for at something like a magpul moe guard to get me started. Thanks for helping a new guy and this site has been a great help!