If the rifle in question wears a mass produced factory barrel, I wouldn't bother following any break-in regimen, if its an expensive custom barrel, its best to follow the manufacturers recommendation. The break-in procedure seems to be directed more towards the chamber than the bore, specifically, the lead, and this is where the hairs left from the cutter and hone spinning across the grain of the steel have an impact first on barrel fouling, and secondly on accuracy. Krieger's explanation of the procedure and its benefits sounds right to me.
Now one of the frequently encountered arguments opposing the break-in regimen is that its a devise created by barrel makers to wear out barrels more quickly so more could be sold. Quality barrel makers don't seem to need greater demand for their products, but if we assumed that was true, just how careful cleaning with a quality one piece cleaning rod attached to a brass jag stabbed into cotton patches soaked in solvent, and passed through a bore guide in the receiver of your rifle, between shots for the first few rounds, then after each group for a few more, for a total of about 20 rounds, could be detrimental to the life of the barrel confounds me. Yet there are those who seem to believe this, as much as others believe in the benefits of a barrel break-in.
There is however legitimate debate over the potential benefits of a barrel break-in, particularly on barrels for big game hunting rifles. MOA accuracy is pretty much now the standard for the big game rifles, a MOA big game rifle has almost no practical advantage over a 2 MOA big game rifle, and there is certainly an argument to be made that one does not need to follow a day long break-in procedure to achieve what will amount to less than a quarter minute improvement on those barrels. The flip side of the argument is that fouling is reduced when the barrel has been broken-in, making cleaning quicker and easier. Does any of that matter? That depends on your expectations and on your point of view.
