May I ask why a good chrome lined barrel is out of the question for a SBR? Are you going to be shooting it from a bench mostly? Why not just build a precision rifle if thats what you are after?
I shoot in F class, Modified F class and F/TR matches yearly. I understand the satisfaction of a accurate, long range rifle. I just dont know why you would be so concerned with the accuracy of a rifle designed for up close and personal use.
As I said above, the most accurate will be a high end custom. Krieger, Lilja, Rock Creek, Obermeyer etc... with a match chamber and headspaced bolt.
Getting ANY AR to shoot .5 MOA consistently is not easy. Even with a premium barrel and match ammo its not easily done. Lots of practice, reloading, shooting fundamentals are involved with that kind of precision. Its not like pulling the trigger on a bolt gun.
If you figure out how, let us know.
ETA: I don't mean to criticize your plans. But if I have a better understanding of what you wanted from the rifle, I can give you better answers.
Last edited by CBMJR; 09/11/13.
