I'm not a firm believer in breaking in a barrel other than I won't shoot a barrel hot. Typically 3 shot group for stuff over 3000 fps, 5 shot group for stuff under 3000 fps, and then a cooling period until the barrel is back to pre-shooting temp.
I do like to use JB bore paste before shooting the rifle for the first time and then every few times to the range until 4 range sessions are completed. It smooths out the barrel from the factory burrs, which reduces fouling overall.