I didn't intentionally post the break-in info offline, newbie mistake, oops! I'll give it another try..
A lot of times the barrel is breaking the shooter in than vice versa. A quality barrel is hand-lapped, and if you think about it, the lapping process IS the break-in process. Not only is the barrelmaker looking for a dimensionally uniform barrel, but a uniform surface finish. Lapping turns the 'grain' of the finish to follow the helix of the twist, so everything flows with the spin. Perhaps a less than quality conscious chambering would result in chatter past the leade, and MAYBE that requires smoothing out, that is my only plausible explanation for a break in procedure.
With that, I'll explain how I break in my rifles. I fire one 'fouling' shot, when the barrel cools I use a patch dipped in copper solvent. Then I shoot a string of 5 shots, in about a 5 minute span, clean, inspect the bore then put the rifle away. After that, I shoot 10 rounds then clean up to the 50th round, and usually I'm done sooner than that. But I can't count much higher than 50, so I'll stick to that, ha. Clean it when it needs it from then on. I'd rather push bullets down the bore anyway.
I don't adhere to this procedure religiously, each barrel is different or has different tendencies, and I basically shoot until I get a feel for the rifle to figure out what she wants.
I never (well,almost never) use a brush on handlapped barrels, never 'fire-lap' a bore I've cut. I never use JB's in my bores, I stick with solvents and flannel patches. There are a lot of different situations, and I employ different procedures for each, I'll save that for another day.
, Art