Barrel break-in for a factory rifle is a waste of time. Break-in for my customs I've stuck with what GAP & Krieger recommend: Clean the throat/leade after 5 rounds to knock down whatever copper built up, and then I just keep shooting till the amount of rounds I decide necessary. That is just what made the most sense to me. The copper seen through the barrel is a result of the copper being molten and sprayed from the contact with the lands. So that is the spot to "burnish".
AR barrels get cleaned at the gas port at 10, 20, 30 round schedule to reduce the/any metal migration cause by the port. Some barrels migrate pretty bad, others barely at all. If one gets a custom 416R stainless and it's not bug holing, I would bet the farm that the metal migration at the port is the culprit. Nitrided and CMV barrels migrate less than 416R.
I've also been using Thoroclean on all my barrels for the past year. I've thrown out all other barrel cleaning products. Using a slightly oversized bronze brush and Thoroclean system, the carbon rings are gone and barrels are spotless in 5 minutes. I ran out of the Thoroflush and substituted "Purple Power" degreaser as I found a degreaser is what comprises most of the flush.