I guess I'm the only one that doesn't endorse ARP's barrels. I've got 3 of his barrel's,and they shoot OK at best. I have a 18" SPR 223,a 16" SIX5,and a 16" 6.8 barrel,and have never been impressed with their accuracy with any bullet/powder combinations.
I just built a new 6.8,and used a White Oak barrel for it. I haven't had time to shoot it yet,but every barrel that I've ever bought from White Oak has shot well under MOA.
Harrison's 6.8 Super bolt is a good piece,but I'll never buy another barrel from him.