The Barrett .50 caliber rifle is a powerful gun. Widely used in the military, its rounds can "penetrate light armor, down helicopters, destroy commercial aircraft, and blast through rail cars," according to a report from the Violence Policy Center, a gun safety group. The Law Center to Prevent Gun Violence describes .50 caliber rifles like the Barrett as "among the most destructive weapons legally available to civilians in the United States." And as of Wednesday, the Barrett .50 caliber is now the official state rifle of Tennessee, joining an illustrious roster of other state symbols including the raccoon (state wild...