It can help a lot with copper fouling to break in a rifle barrel. With that said, there are some chrome moly barrels that are rougher than a cob and you will never get them to clean up.
On a hand-lapped barrel, it normally will take around 10-shots to clean-up. Shoot one shot, patch with a copper removing chemical such as CU+2 bore tech or something similar until all copper is removed and repeat.
Some SS barrels will take 15 to 25 shots. If 25 rounds doesn't clean it up - well, it probably never will clean up but those 25 rounds fired will probably assist in quicker clean up times for the life of the barrel.
For most commerical grade barrels I doubt any of them will clean up but taking a couple hours to break-in a barrel should reduce your cleaning time in the future.
Most of my bench rifle barrels would clean up with three patches - my varmint rifles with Wiseman and Shilen barrels clean up with about 10 to 12 patches.
On another forum there was a thread about taking 2-days to get all the copper out of a barrel. Now that had to be one rough barrel. In the old days it took a full day and then some to remove all the copper from a 378 weatherby that fired 50 to 60 rounds but that was with Sweet's 7.62 (slow acting).
In benchrest - barrel break-in was done relative to quick clean-up times - did nothing for accuracy. We usually fired 7 to 12 rounds in 7 minutes or less and then cleaned the barrel, reloaded the cases and prepared for the next string. Nice to run three patches and done - spend the rest of the time reloading, viewing targets on the wailing wall and visiting.
