A half-century is a long time for a standard-issue weapon such as the M16 to remain 'standard.' Here is a quick look at three M16 variants that saw service.The M16 has served as the United States’ primary service rifle for nearly half a century, and in that span of time, many variations of the rifle have been created. Some were prototypes that never went beyond the testing stages, others represented improvements to the original design, and some simply defy easy description. While a complete history of all the unusual M16 versions could fill a book (and probably have), here is...