I would agree with looking on ar15.com! I'm on there and there is some good advice if you can wade through some egos.I don't buy that Oly is onlycomplete built ar,My cmmg is pretty darn complete enless I wanted special parts.CMMG barrel,same lower upper is theirs,I just wanted some things different.There's alot of non-colt guns out there that are well built but still affordable.I don't care what brand as long as function is built in!