Corbin Bore Lap is used to polish and condition either a new barrel, to remove tool marks and burrs, or to repair a rusted or badly fouled older barrel by removing foreign matter. Unlike most abrasive lap compounds, Corbin's synthetic sapphire uses flat plates of about 30 to 40 micron diameter, which tend to pack tightly against the bore with their flat sides toward the rifling. Their edges then pry and cut off anything that projects from the surface, while the smooth sides slide along the surface and follow the rifling with far less wear than even some popular bore cleaners. To use it, apply to a cotton patch, wrap the patch around a 1-caliber undersized brass brush, and stroke one pass through the barrel by going two inches forward and pulling one inch back until the patch emerges.