I think most shooters misunderstand the term "barrel break-in" and think it aids accuracy.

The purpose is to remove any slight irregularities within the barrel in an attempt to make barrel cleaning easier/faster in the future.

Your custom or commercial barrel comes with minor or major tool marks etc. - this is what you're cleaning up to prevent major copper fouling in your rifle barrel. Some clean up nicely, others not so much while some are just so rough it's just going to take awhile to remove the copper build-up.

Most of the consistent sub-1/4" group barrels out there that I am aware of are select match grade, have been hand lapped and stress relieved - so not much break-in is needed but I will still do it, as 8 to 10 rounds doesn't take that much effort.

If barrel break-in aids the accuracy of your rifle - then you are truly blessed, as it won't for the majority of rifles.