The fine folks at Ballistic Advantage well know for their match grade 6.8 barrels also manufacture barrels for just about every other AR15 caliber from .17 to .308
Shilen is well knows as makers of some of the finest rifle barrels on the planet. It's best to have your bolt fitten and headspaced to the barrel. Brownells is offering Shilen barrels with matching bolts.
Below is a list of the finest barrel makers in the industry. You would be hard pressed to find a champion top level rifle or AR15 shooter that isn't shooting a gun with a barrel from one of the manufacturers listed below. These barrels are often found on the most accurate AR15 rifles and uppers from folks such as Fulton Armory (Krieger) and Rock River Arms (Wilson)