Okay so I am starting my first AR build and am looking for help making a parts list. ? Are different companies compatible with others? ( like can I mate a RRA stripped lower with a bravo company upper and Daniel deference hand guard?) for example Can anyone give me some help on building an upper receiver? Parts list? I know that I want a 14.5 in barrel and adjustable stock. But those smaller goodies will come later. Thanks for the help !