I am not criticizing the shoot one and clean break-in approach, but I quit doing it a couple decades ago and my barrels shoot just as well. They shoot better actually, but that is because I load and shoot better than I did many years ago.
I don't know how long past 100 rounds I can go between cleanings, but I do know that hard carbon really starts to build up after 100-150 rounds.
To be honest, I don't know that hard carbon is an issue, but cleaning it out with JB every 100 rounds isn't a big deal and I don't want to risk losing accuracy in a match.
On the other hand, a friend, gunsmith, and competitor who doesn't put much effort into cleaning at all shoots exceptionally well.
The more I do this, the better I shoot but the less I know for certain.........