I am looking for an add on rail that will extend from the rear of my LMT M4 flat top upper receiver all the way to the other end of my YHM 12.5" free float tube. I want to A( Lock the Float tube and the upper receiver together and B( I want to raise my scope up about a half inch. I have seen a few in pictures on web sites in the past but can not find anyone who currently makes and / or sells one. The PRI and the Armalite rail systems for their respective free float tubes will not work I allready checked. Thanks for your help in advance.