No one has pointed out that "cleaning'' means all the copper is removed before shooting again and that a quality rod and a good bore guide is required or you may be damaging the bore because of your cleaning method.
Several barrel makers post a ''break in'' procedure on their website.
With quality hand lapped barrels there is very little to break in... only the throat area that was freshly cut with the reamer.
Whether breaking a barrel in or not has any benefit or not has not been proven or dis proven. If proper procedures are followed it will not harm anything. At worst you are out some time and a few bullets..
It is a never ending controversy with strong opinions.
Following is a procedure I compiled from various sources. It seems as good as any...
Breaking In A Barrel - Read fully before starting the procedure
When cleaning, always use a good bore guide and a good rod.
Start with a clean, lightly lubed barrel, fire one shot, then run a loose patch through with Sweets 7.62 or any other solvent that will “eat” jacket fouling. Saturate the bore and let it sit a few minutes. Sweets indicate jacket fouling with a blue colour.
Run patches through to dry the bore and then wet patch it again and saturate the bore. After a few minutes dry patch it again. Repeat until the jacket fouling is removed (no blue patches). That means the barrel is clean.
After cleaning with Sweets, brush with Hoppes #9 and dry patch the bore and then leave it slightly lubed with a wet patch of Hoppes #9 before firing.
Then fire one more shot, and repeat the above procedure. Do this for a total of 10 shots, and then proceed to fire 2 shots and then clean as above, for 10 more shots. (For a total of 20.) The barrel is now broken in. It should be cleaned after every 20 or 30 shots there after if possible, or less often if fouling is not a problem.
You will find when the bore is broken in properly; the cleaning procedure is very quick, because there is very little jacket fouling in the bore.
I prefer Sweets 7.62, because it shows “blue” if there is any jacket fouling. I never use a copper or bronze brush with Sweets, because it will eat them, and give a false blue indication of fouling. I never let any other chemicals mix with Sweets. That is why there is a lot of dry patching and swabbing with rubbing alcohol and dry patching between switching chemicals.
For storage after cleaning with Sweets, dry patch and then swab the bore with several patches using rubbing alcohol; this will dissolve any remaining ammonia. Then lightly oil the bore.