The reason McMillian don't recommend breaking in barrels is he's talking about top quality barrels. Naturally the rifle factory cannot afford to use top tier barrels. Tooling marks or burrs are not removed in most factory barrels before shipping. Hand lapping removes all these tool marks (cut rifling-rare nowadays) and burrs. All premium barrel makers hand lap the barrel as a final process. That means with a factory barrel, it highly likely needs breaking in to remove all the burrs & burmish the bore. Breaking a barrel in does the same thing as hand lapping. I break all the barrels in on factory guns.

The exact method you use is much less important than the fact you're breaking it in vs not. I clean it between every shot for the 1st 10-20 shots,depending on how rough it looks through a bore scope. Then clean between every 3 shots for another 21 rounds, then you're done. To those naysayers that don't believe in breaking in ANY barrel-I ask them to look at the inside of a barrel with a borescope at 400x-600x, THEN tell me it ain't necessary-especially on a budget rifle.