I think this is key.
If I've got it right, barrel break in is recommended for the upmost accuracy - for example in benchrest and maybe F Class.
I compete in 'cross the course'. If/when I shoot 1/2 MOA groups [prone with a sling], everyone's excited. I have no idea whether my lack of barrel break in makes my barrel capable of only .2 MOA vs .1 MOA if I had broken it in.
I think the same thing could be said for PRS.
I agree with this too. In practical terms that I think most can relate to...we spend good money on premium bbls and gunsmith work, for starters. Now, the way I see break in is this. Say you have a 4 groove bbl and a really good chamber job. You go out and put say 30 rounds down it and go home and clean it perfectly, as new..or not.
Lets say 3 of the lands never collected the very first bit of copper but the 4th did. From first shot on, it just got a little worse and worse but you never saw a difference in how it shot over that time. Hey, it's new and you probably don't know its potential yet anyway, right.
Well, over those 30 rounds, 3 lands broke in nicely and they are gorgeous...no problem at all. But, those first few shots likely give more throat wear that the rest of the rounds you put through the bbl in a "reasonable" life span.
So, we have 3 lands that wore away a bit and broke in. How does the 4th ever catch up? It was shielded from the heat, flame and friction from the first shot on.
Bottom line, if you're happy for your use, rock on. I do think one barrel can give more or less benefit than the next one, from the same break in process and depending on your discipline, it may VERY well never matter one iota, with the best shooter. If you're shooting off of a fencepost...forget about it other than maybe a rare instance. If you shoot at a fairly high BR level, it may well be quantifiable...or not, too. Ya got no base line to compare it to, right?
But, if you get copper fouling, I would say it's unfair to blame the bbl maker at all, none. The reasons have already been covered. I'd say it's a small price to pay to ensure you get your money's worth from you're hard earned money in the bbl as well as the chamber work. And, ya gotta be fair to the smith too. It takes next to nothing to start a little copper fouling and then copper builds upon itself. As well as, what if you furnished the reamer or he did. Kinda out of your and his control but a proper break in should either optimize things in a relatively short time or...tell on the smith, the reamer maker, or less likely, the bbl maker...but he's the most likely to get the blame, wrongfully so most of the time.
We are blessed with several very, very good barrel makers who for the most part, bend over backward to make sure the customer is happy but they should never have to bend over forward, due to someone not following a proper break in of the throat.
Long winded..sorry, but I think this is a very fair and real assessment of why we should do a proper break in. I can assure you that it's not to sell more barrels. That's just ludicrous. I'm sorry, but it is.. and most of that originated from the internet keyboard shooters, so I don't blame everyone for believing it...to a degree. I mean, all it takes is one true expert to be wrong one time publicly or whatever, and it becomes gospel because so-and-so said it.