If you are not handy with tools, send the barrel out. It can probably be repaired without destroying the finish. If you undertake the job yourself, I would suggest center drilling in a milling machine with a rigid spindle(as opposed to using a drill press)using a left handed center drill. Then drill through the remaining length of screw with a left handed drill. Because the center drill and the body drill are turning counter clockwise, they will both tend to remove the remaing screw stub. If the stub is not removed during drilling, use an extractor after drilling. I agree with the rest of the advice given by others.