The Army adopted its battle rifle in 1963 and has spent 55 years looking for a replacement for the M-16 and its variants. They might have found it in Martin Grier’s Colorado Springs garage. Grier, a self-described inventor who has worked at a local bed and breakfast, built the new “ribbon gun” with a hobbyist’s tools. It looks like a space-age toy drawn by a fifth-grader. But goofy origins and cartoon-looks aside, this could be the gun of the future. The Army is studying Grier’s gun and has ordered a military-grade prototype. ... The specifications are incredible, four 6 mm...