Breaking in a barrel properly is the only way to insure consistant lasting accuracy out of a gun.

It is an absolute must for any rifle! (period)

The most important factor in the breaking in process is to not let the barrel get to hot but to run a boresnake down without solvent after every shot for the first 20 and then after five and then after ten. Then when it's cooled give it a good cleaning making sure to remove all copper and lead deposits.

There are other processes but this is what works for me.