When Christian Michael Mackey drove to a parking lot in Grand Prairie to allegedly sell an AM-15 rifle on Jan. 29, he didn’t care that the person buying the firearm was a self-proclaimed felon. What Mackey wanted to know was whether the buyer was “based,” meaning a fellow traveler of the white nationalist movement. The buyer was a paid source for the FBI, the Department of Justice said in a press release on Monday. Agents arrested Mackey and charged him with the unlawful sale of a firearm. He appeared in court on Monday, and his detention hearing is set for Wednesday.