I'm in the process of making an AR-15 SBR. I am thinking of getting this upper from Del-Ton:
http://www.del-ton.com/SearchResult.aspx?CategoryID=26
2nd upper, the 11.5".
On the AR that I have now, I have a Bushmaster Lower with a DPMS 20" upper w/chromed barrel. I will say that the DPMS is a very good product, I am very happy with it.
Wayne