The Bureau of Alcohol, Tobacco, Firearms and Explosives is in charge of determining whether a gun model is legal, but the agency won’t say much about its criteria.
Despite overseeing an industry that includes machine guns and other deadly weapons, ATF regulations for the manufacture of weapons are often unclear, leading to reliance on a secretive system by which firearms manufacturers can submit proposed weapons for testing and find out one at a time whether they comply with the law, critics say.
The ATF recommends that manufacturers voluntarily submit weapons for case-by-case determination. But those judgments are private and, it turns out, sometimes contradictory. Critics say nearly identical prototypes can be approved for one manufacturer but denied for another.
That process, known as “letter rulings,” results in various findings about what makes a weapon. Program critics, including the ATF’s former assistant director of criminal investigations, said one determination contended that a shoestring was a machine gun.