I purchased a complete upper used from a gentleman who said that he special ordered his upper from colt. It is a flat top upper and he got all but rear sight with it. the rear sight is arm lite which he said that he had already bought new for another upper but did not use it. Mine has a 16 inch barrel. I put the upper on a Double Star complete lower and it shoots great. I would check with Colt about ordering one. He told me the comlete upper without rear sight was over $500. I was lucky because he had shot less than 100 rounds through it and sold it for $300 just so he could buy a SAR 1 at a gun show! Hope this helps.