I got lucky when I built my son's heavy barrel 223 using a factory stainless fluted barrel. I's a 1 in 9 twist and loves the 75 gr A-Max bullets. He shot at 400 yards for the first time Sunday and managed a 3.69" group at that range after getting his elevation right. He fired 6 more shots and all those averaged 4.59" with five going into 2.73".