I recommend a google of “Kreiger barrel break in”. A look at the equipment lists among the top 20 finishers in most International Bench Rest Shooters” matches provides a pretty strong argument that Kreiger knows barrels.
Kreiger says that bore BI is not necessary in lapped bores
but when the chamber is cut, reamer marks are left in the throat which lay across the direction of bullet travel. Until these “marks” are ironed out they pick up copper from the bullet jacket which is vaporized and deposited in the bore just forward of the chamber. Since copper adheres to copper very well, a build-up can occur which becomes difficult to remove later. Hence, Kreiger recommends a shoot-and-clean cycle to BI their barrels.
I have never heard any credible claims that BI itself improves potential consistency, but it is a well known fact that as barrels get increasingly copper fouled, accuracy falls off, so it makes some sense to get rid of that “early” build up. I have no metallurgical expertise, but make the assumption that copper deposited in the bore which condenses from a vapor, adheres to the barrel steel better than the copper deposited by friction contact?
Kreiger also observes that copper adheres to CM more than SS.
In the end, what each believes is best for their barrel is the practice they will follow. Fact is, most barrels will out shoot their owners. Personally, I have no pride and will take every advantage whether it be real or imagined to shoot my best
. So, I do a 5-10 shot shoot/clean cycle with all my new barrels.