Here is a little longer quote (I got from Accurateshooter.com):
There are three schools of thought on barrel break-in. First, famed barrel-maker Gail McMillan believed “less is more”. Simply shoot five shots, clean, shoot another five shots, clean, and then clean every 5-10 shots or so over the life of the barrel. He argued that the “one-shot, one-clean” ritual was a gimmick devised by barrel makers to wear out barrels more quickly so they can sell more product. He rightly points out that every shot down the tube just reduces your barrel’s maximum accuracy life.
The second school of thought, with Krieger in this camp, suggests to shoot and clean after every shot for 5 shots, then again after every 3 shots, until fouling is not noticeable: “Initially you should perform the shoot-one-shot-and-clean cycle for five cycles. If fouling hasn’t reduced, fire five more cycles and so on until fouling begins to drop off. At that point shoot three shots before cleaning and observe. If fouling is reduced, fire five shots before cleaning.” Full Article.
The third and last school of thought says to clean aggressively after every shot for a dozen shots or more, and to use an abrasive lapping compound such as JB after each of the first few shots. The idea is that this will “polish” up the throat to reduce fouling and enhance velocity. Along with bore paste, you can fire-lap the bore using bullets impregnated with fine abrasives. This is done most easily with the Tubb Final Finish system which contains bullets with five different grit levels. So, what procedure should you follow? We think Gale McMillan is probably right, but he was talking about fine custom barrels that are already hand-lapped to a mirror finish. If your barrel is rough to start out with, the other methods have some merit. We would not use Final Finish on a hand-lapped custom barrel however.
----Kreiger also knows a thing or two about barrels, then there is a guy that uses a lot of barrels David Tubb, he thinks McMillan is"probably right" when talking about fine custom tubes. There is more than one answer.