Perhaps. Orthopedic surgeons routinely use tourniquets to control bleeding during surgery. In the above hypothetical situation, you are alone with a massive gunshot wound to a long bone and are symptomatic from blood loss. Time to use a tourniquet if direct pressure will not stop the bleeding. A GSW to the femur (in this case a high powered rifle), good chance are you are going to lose the limb anyway. The decision to amputate is based on whether or not the extremity is viable.