Breaking in a barrel is like cryo treatment or moly coating; some guys believe that it improves performance while others don't. Hart bbl mfg sais it is unnecessary but Lilja bbl mfg feels differently. Here is how it is done according to Dan Lilja: Break-in Procedure For an effective break-in the barrel should be cleaned after every shot for the first 10-12 rounds or until copper fouling stops. Our procedure is to push a cotton patch that is wet with solvent through the barrel. This will remove much of the powder fouling and wet the inside of the barrel with solvent. Next, wet a bronze brush with solvent and stroke the barrel 5-10 times. Follow this by another wet patch and then one dry patch. Now soak the barrel with a strong copper removing solvent until all of the blue mess is removed from the barrel. The copper fouling will be heavy for a few rounds and then taper off quickly in just one or two shots. Once it has stopped or diminished significantly it is time to start shooting 5 shot groups, cleaning after each one. After 25-30 rounds clean at a normal interval of 10-25 rounds. Your barrel is now broken-in.