HUDSON - For years, marksmen have used a technique called bump firing: shooting a semiautomatic rifle from the hip and allowing the weapon's recoil to pull the trigger. With the assault-weapons ban keeping most fully automatic weapons out of their hands, it was one of the few ways for enthusiasts to enjoy the thrill of firing a machine gun. Bill Akins found a way to simulate that action by inventing a device that mechanized the recoil resistance of a semiautomatic rifle to fire more rapid, and accurate, bursts of bullets. The Hudson man spent nearly a decade designing the Akins...