I have written this article for LRH some time ago, about this very topic, PLEASE take the time to read it with an open mind and then you MUST read the following forum discussion linked on the last page of the article.
Both will explain and answer many of the common questions asocciated with "barrel brake in". If your not going to read it all then don't bother to read any of it. It is not a topic I will debate.
Custom Barrel Care At 17X
My feelings on abrasive paste are still quite strong, although I have now used Iosso in my F-class guns about every 350-400 rounds to remove some carbon in the first 6" of barrel, very limited number of strokes. 1 patch back and forth 3-4 times.
One of my team-mates has a 260 rem f-class gun that is now on 2300 rounds fired. It had really lost it's groove just before the team state championship. He scrubed the first 6-10" agressivly with JB in hopes of A. smooth up the aligators back, and 2. get rid of neglected carbon fouling. It worked and the gun started shooting again. This is an extreame case and should be done only for this type of condition.