Montana, 17 other states file brief in lawsuit challenging bump stock rule Bureau of Alcohol, Tobacco, Firearms, and Explosives By: MTN News and last updated 2021-08-03 17:18:54-04 HELENA â Montana and 17 other states have joined together on an amicus brief (friend of the court) in a lawsuit challenging a Trump administration rule criminalizing bump stock accessories. Bump stock devices gained national attention when one was used in the 2017 Las Vegas mass shooting that left 59 dead and hundreds more injured. On February 20, 2018, President Trump issued a memorandum instructing the Acting Attorney General âto dedicate all available resources to⦠propose for notice and comment a rule banning all devices that turn legal weapons into machineguns.â