From the Document: "Congressional interest in regulating 'bump stock' devices grew after authorities discovered that the perpetrator of the October 2017 mass shooting in Las Vegas had attached to his semiautomatic firearms an accessory that allowed his rifles to effectively mimic the firing capabilities of a fully automatic weapon (e.g., a machine gun). But to date, federal legislation has not been enacted that expressly regulates bump stocks. At the administrative level, though, the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) banned these devices--effective March 26, 2019--in a final rule published in the 'Federal Register' 90 days earlier on December 26, 2018. ATF achieved this ban by classifying bump-stock devices as 'machineguns,' as that term is defined in the National Firearms Act of 1934 (NFA) and the Gun Control Act of 1968 (GCA). Several bump-stock owners and advocates challenged ATF's rule in multiple lawsuits, arguing, among other things, that ATF promulgated the rule in violation of the Administrative Procedure Act (APA). In one of those lawsuits, 'Guedes v. ATF,' the U.S. Court of Appeals for the D.C. Circuit (D.C. Circuit) upheld a lower court ruling that declined to preliminarily enjoin the rule from taking effect. This Sidebar explains the statutory framework for regulating machine guns, discusses ATF's final rule, and examines the APA-related litigation."
CRS Legal Sidebar, LSB10296
Congressional Research Service: https://crsreports.congress.gov/