There are break-in procedures, and cleaning with JB or Iosso Bore Cleaner will get them to progress a little better than just patches and solvent, but they don't truly lap the bore.
For true lapping you have basically two alternatives: hand lapping and firelapping. The first normally uses a lapping slug on the end of a cleaning rod that is cast into the muzzle of the bore by plugging the bore back an inch or two with patches or paper and pouring molten lead into it. Grooves similar to lead bullet lube grooves are cut into the cast slug with a knife or a gouge to hold abrasive compound. The lap is loaded (the grooves filled) with abrasive and run back and forth in the bore by hand. It's s common to use something like 320 grit silicone carbide lapping compound (Clover compound, for example). The slug is usually pure lead so that when it encounters a constriction it is narrowed and does not spring back out after passing through it. In this way all abrading on subsequent strokes is only in the tight spots. When you feel it stop cutting tight spots, you can bump the lap back up with a brass rod and hammer, and go at it some more. You keep repeating until the bore has no more tight spots and the lap feels smooth down the length of the bore.
The other method is firelapping. This involves shooting abrasive embedded bullets through the bore with very light loads that get low airgun velocities (300-500 fps). The lapping bullets are usually cast bullets in the hardness range of 10 to 12 BHN. This number range is a compromise. It doesn't limit itself to cutting constrictions as completely as pure lead laps on a rod, but it is malleable enough that it doesn't lap the wide places nearly as hard as the narrow ones. The reason it isn't pure lead is that where a pure lead hand lap can be pushed through a constriction by rod without bumping up, when you have even firelapping load pressures on the base of a pure lead bullet it will bump up to rub the wide spots as well as the narrow ones. At the other extreme, an alloy bullet of higher BHN is surprisingly elastic and will go tightly into the bore and stay tight all the way down its length, thorough narrow places and wide ones. That tends to remove material evenly everywhere. You don't want that because, while it widens tight spots, it widens wide places equally, so you don't level off major irregularities; you just smooth those shorter than the length of the slug. When you are done firelapping, irregularities are gone and it leaves the bore very slightly tapered down toward the muzzle. Maybe a half thousandth or so. This is considered desirable for accuracy, especially when the bore is to shoot lead bullets.
Either lapping method will reduce metal fouling, making the bore easier to clean. Firelapping has the advantage that in addition to introducing the slight taper, it also cleans the throat up. Hand lapping does not normally clean the tool marks off the throat because the rifling is cast into the slug when you pour the lap.
The board sponsor, Beartooth Bullets, sells a firelapping kit, here.
technical note (and I hope I haven't posted this already)... some barrel makers have their own "lapping" procedure. If you have a Kreiger barrel, it's best to read their thoughts on their barrels. I normally use Kreiger when I can. Got 2 M14 barrels on the shelf.