Taser International, whose electrical guns are used by thousands of police departments nationwide, says that a federal study endorses the safety of its guns, but the laboratory that conducted the research disagrees. Taser said last month that the government study, whose full results have not yet been released, found that its guns were safe. Since that statement, the company's stock has soared and its executives and directors have sold $68 million in shares, about 5 percent of Taser's stock and nearly half their holdings. But the Air Force laboratory that conducted the study now says that it actually found that...