Abstract: A method for lapping of gun barrels on fully assembied firearms is provided using cartridges fitted with lapping bullets impregnated with abrasive. The present invention provides a process for simultaneously impregnating a quantity of lapping bullets with an abrasive, in which a quantity of unlubricated bullets are placed in a tumbler with steel balls and quantity of the desired abrasive. The speed of rotation of the tumbler, and the shape of the tumbler are selected so that the bullet/abrasive/tumbling media mix folds on itself, thus providing an even impregnation of abrasive on the bullets and minimizing any deformation of the bullets. The mixture is allowed to tumble for a period of time, typically about an hour, after which a sufficient quantity of the abrasive is firmly embedded on the surface of each bullet. The abrasive impregnated bullets can then be coated with a protective and lubricating finish, such as carnauba wax, if desired.