All with barrels the shooter didn't have to improve on by breaking
them in.
That may be true but...
McMillan himself explained why a barrel settles down and shoots better after a couple of hundred rounds if a dull throater left burrs.
And..
But like a fine new tool, it always works better when "broken in" and lightly oiled afterwards!
Maybe if every barrel was made to the same level of quality as a McMillan barrel this stuff wouldn't be true. And if they were McMillan barrels wouldn't have won so many things, set so many records, yadda yadda yadda.
"MY" best rifle shot better after I had shot maybe 150 rounds through it. I never did any of that shoot 5, clean, shoot 5, clean two step stuff. I just shot it and cleaned it a reasonable amount (which isn't very much for me BTW). And presto changeo it started getting gradually better after about 50 rounds right up until about 150 rounds when it levelled off.
To me "that" is breaking in a barrel. You're knocking off those little imperfections that maybe McMillan doesn't have but most rifles made on mass production equipment do have. If anyone thinks that every company changes the cutting head on a bore cutter after it shows the slightest bit of wear raise your hand about face high and smack yourself in the forehead. Because you should have just had a revelation. Unless your barrel company is McMillan the chances are they don't change those bits until they reach a certain level of tolerance.
Cutting steel can leave little burrs here and there if the bit isn't "perfect" and few bits are perfect. In a perfect world we would all have McMillan perfect barrels but I doubt even McMillan sells 100% perfect barrels in this imperfect world.
I don't buy the whole razzamataz about cleaning every 3 rounds, stand on your head, sacrifice a chicken, blah blah blah but I do believe bullets have a way of knocking off those tiny little burrs that can make a big difference in accuracy.
In short I don't think either side is 100% wrong or 100% right here. I think it's a matter of how good your barrel actually is when you get it and how well shooting a few bullets through the barrel will actually help it.