(CNN) - In his 23 years with the Bureau of Alcohol, Tobacco, Firearms and Explosives, Dan O'Kelly was one of the agency's top gun experts. He served for five years as the lead firearms technology instructor at the ATF National Academy, where he co-wrote the curriculum for incoming agents. These days, however, O'Kelly is using his formidable firearms expertise and institutional knowledge of the ATF to take aim at his former employer. He's at the center of a brewing legal dispute that federal prosecutors say has the potential to upend the 1968 Gun Control Act and "seriously undermine the ATF's...
