Brownells Gun Techs Extraordinaires Steve Ostrem and Caleb Savant tackle a thorny topic: breaking in a new barrel. What IS breaking in a barrel? And WHY do it? The rifling of a freshly machined barrel has microscopic burrs and sharp edges. "Breaking in" is the process of putting bullets down the bore to smooth out those rough spots. The goal is to round down the sharp edges so they're not stripping copper off a bullet as it travels the bore, which leads to fouling that leads to reduced accuracy and inconsistent groups. In a very minor way, you're actually lapping the barrel. The breaking in process works best on cutrifled and buttonrifled barrels. Cold hammerforged, chromelined, or nitrided barrels such as commonly found on AR15s don't benefit from it. Pistol barrels really don't need to be broken in because largerdiameter bullets are not so much affected by tiny variations in the bore. Likewise, breakin is more helpful for a .17, .20 or .22 caliber rifle than a .45 caliber rifle.

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