An anonymous reader writes: Researchers from the U.S. Army Armament Research, Development and Engineering Center recently patented a new type of bullet capable of self-destructing after traveling over a predetermined distance. The idea behind the new and advanced projectile is that it might help limit the extent of collateral damage (read: innocents dying) during battle or in other operational settings and environments. As for how it all works, the U.S. Army explains that when one of these limited-range projectiles is fired, a pyrotechnical material is ignited at the same time and reacts with a special coating on the bullet. "The pyrotechnic material ignites the reactive material, and if the projectile reaches a maximum desired range prior to impact with a target," the Army writes, "the ignited reactive material transforms the projectile into an aerodynamically unstable object." The researchers add that the desired range of its limited-range projectile can be adjusted by switching up the reactive materials used. Put simply, the Army has come up with what effectively amounts to a self-destructing bullet that is rendered ineffective over certain distances.