Critics said the M-14 was what happened when the U.S. government took many years and spent millions of dollars designing a rifle that was really just a glorified M-1 Garand from World War II. The M-14 was the U.S. military’s last battle rifle. It appeared in 1959—the contemporary of the Pentagon’s first jet fighters and ICBMs. With its heavy steel parts and walnut stock, the M-14 looked positively archaic. It was hardly a Space Age weapon. And it only endured as America’s battle rifle until 1970, when the M-16 completely superseded it—the shortest service record of any U.S. military rifle...