Hopefully, you don't oil it internally every couple of weeks!i didn't oil the gun for a couple weeks.
Unless primers are staked or crimped in they will back out a hair when fired then the pressure of the burning propellent pushs the case back which seats it flush again, the case then springs back into shape and rebounds a hair from the breechface. If theres no bullet or powder then the primer remains backed out and will rub against any tool marks or the firing pin hole in the breechface.Evidently the primer blows back if there is no bullet in the shell?