Check out this thread, it may shed some light:

http://benchrest.com/forums/showthread.php?t=46802&highlight=barrel+break

I have a very, very, very hard time believing that the Army marksmanship team rarely cleans their rifles. I'm borderline on calling BS on that!!! I know a fellow that was on the team and he is one of the most anal people I know when it comes to cleaning his rifle.

I know several BR competitors and they all clean there rifles between strings. At a BR match there is always two things going on.... People loading ammo trying to match conditions, and competitors cleaning their rifles.

Does a custom barrel that has been hand lapped require break in? maybe, maybe not but I do it anyway.Would a mass produced factory rifle barrel benefit from a break in? You bet!