Not all barrels are equal. Mass produced factory barrels are usually not concentric. The crown and muzzle threads being out of alignment with the bore. This degrades accuracy and its why we dial indicate our barrels in to .0002'' (.005mm) before chambering, threading and crowning. The image below details the process of truing up a factory barrel to be concentric. Initially the crown is completely out of alignment but is eventually correctly aligned. Unfortunately most gun shops and gun assemblers don't have the ability or knowledge to do this.
