Steve,
Where in SC are you? I have an offer for you. I live in Monroe NC and work in Rock Hill SC. I'm more than willing to let you try my DPMS upper on your lower to see how tight it will group. It would sure let you know how well the DPMS 16" HBAR barrel will group rounds. Bring your bore scope and lets compared the finish in the bores side by side.
I have a friend in Lancaster SC that lets me shoot in his back yard. We have a 55 yard range setup with railroad ties as a back stop and steel plate targets on it. We do have access to a 300 yard range, not far from his house, but we don't have the target stands finished yet. Let me know if your interested. It would be great to meet a fellow brother from the board. Between the two of us, let see if maybe we can save you some time, money and aggravation in the process.
Shane