What do you mean by lapping? A barrel maker laps a barrel after cutting it, by pouring molten lead into the barrel and making a slug (the lap). This is on the end of a rod. Then he loads the lap with polishing compound and gets after it. As the lap wears and the bore gets polished, he might need to recast the lap to better fit the barrel, as he progresses thru finer grits of polish.
Now, if you mean, how to polish a new rifle barrel before shooting, here's what I do. Load a cleaning patch with JB compound and give the bore 50 strokes. If it's exceptionally rough, you might want to start with 25 strokes using flitz, then JB, and finally Remington Bore cleaner, and then solvent of your choice to clean all the gunk out. Then shoot the barrel and see if it copper fouls or not. Repeat as required (probably won't be required).
HTH, Tom
