hand lapping is not done with patches, have fun,do things your way,but it is a rare person who has the knowledge and skills to improve a factory barrel,
IMHO,the time to try lapping a bbl yourself is when the bbl is unacceptable and you have nothing to lose.I bought a pre threaded,short chamber cheap bbl once.It copper fouled horribly.A peak with a 10X loupe at the muzzle showed the rifling button had smeared the steel like cheeze.
I charged some cast 30-30 bullets with some very fine diamond lapping compound I used to polish molds with.It was successful,that barrel shot well.
I hand lapped a 40 cal cheap bpcr bbl because when I slugged the boreI there were tight and loose spots.I used a method described in a circa 1930s gunsmith book,I think Clyde Baker.A tapered brass large woodscrew is fitted to a cleaning rod.Within the bore,molten lead is poured around the screw.Without removing the lap from the bore it is allowed to protrude enough to be charged with abrasive.Turning the screw in a bit expands the lap.
After my time and trouble,I came to the conclusion it is better to buy good barrels.I truly do not believe I can improve the Badger .50 that will soon be in a Rolling block.I don't think I can improve a Douglas,Shilen,Lilja,either.I have built rifles with all of those and they shoot.