a sliding safety device for use in ar - 15 style and type of semi - automatic rifles is disclosed . the sliding safety device having cylindrical end portions is configured to prevent the discharge of semi - automatic rifle when the device is in a “ safe ” position . additionally the invention includes the method of retrofitting the sliding safety device into the lower receiver of a semi - automatic style or type rifle after removal of the standard rotating safety selector device that has been in use since the inception of semi - automatic rifles of the ar - 15 style or type .