A quality barrel from Compass Lake Engineering in Florida (Frank and Theresa White) with a new bolt headspaced to the barrel combined with a quality free-float tube (again, Compass Lake for a Service/Match rifle or a DD for an SDM type gun). Anything else (triggers, sights,) will NOT make the gun more accurate only help YOU as the shooter in your job.
Good ammo helps, BlackHills is the standard by which most others, including handloads are judged.
There are others that make nice stuff but CLE makes, without a doubt exceptionally accurate and reliable equipment.
-k

