Abstract: The Upper Receiver Device (URD) is a safety invention to protect a left handed person from shooting a right handed rifle and the hot spent cases striking them in the face, eyes and neck which may cause burns, blindness and other injuries. The left side Upper Receiver Device (URD) is new and an improvement in the left handed rifles. The Lefty URD is different from those used by right handed rifles as you look at them in the right and left side. The bolt lock, carrier of the Lefty URD is different in the number of ridges. The bolt lock, gas hole and the internal components are different and must be manufactured to the Lefty URD specifications. We reference the AR-10 and other rifles with various substitutions and modifications this invention applies to other firearms and is included in this disclosure.