I'll probably be doing this sometime soon myself. I wanted a Sig 556 but they're too costly.
oh I am sorry, I forgot to say that the barrel was a bushmaster, the furniture was bushmaster, the upper I dont have a clue I bought it from an individual, it was new. the lower was an essential arms and the bolt carrier was a colt. all of the parts were bought from people, no gun shops involved. and it cost me less than 500 dollars. and I want another one too