I have always liked the CMMG 11.5" H-barrels with the 1/7 twist. Problem is that I thought for sure that I had put one back when I sold so many of them years ago. Then when I built this F/A lower, I pulled the upper out of the box and it was a 16". It was in the wrong box, for the one I put aside for myself. So I had to use this CMMG upper that I also saved. Problem is that the 11.5 ones from them are not easy to get now. I will get some for my other F/A builds, it just may take a while. I am really happy, I tested the timing using the 1/16", 3/16", 5/16" punch method and it is right on.