ALBUQUERQUE, New Mexico, June 16 -- The U.S. Department of Energy Sandia National Laboratories issued the following news release: * * * B61-13 first production unit completed ahead of schedule * The first production unit of the B61-13 gravity bomb has been completed about a year ahead of schedule, marking a major milestone for Sandia National Laboratories and the broader U.S. nuclear security enterprise.  Two technologists at Sandia National Laboratories place the final screws in a B61-13   more