Three years ago, the nation's capital region lived in fear of a pair of snipers who killed 10 people and wounded three in random attacks with a Bushmaster XM-15 .223-caliber telescopic rifle - a gleaming civilian version of the Army's basic M-16 assault rifle popular with recreational shooters. In the aftermath, the rifle was traced to a shoddy gun dealer who claimed he somehow "lost" that war weapon and some 200 other guns to the underground market. Victimized families sued in grief and outrage and won $2.5 million in a settlement that most Americans - except Congress - would pronounce...