In a case issued on Sept. 7, 2021, the U.S. Marine/Navy Court of Criminal Appeals found that "bump stocks" were NOT machine guns, and reversed a conviction which presumed they were. U.S. v. Ali Alkazagh, 202000087. This determination is consistent with the ATF, which had determined that bump stocks were not machine guns on ten separate occasions from 2008 to 2017. It reversed that position in 2018, claiming bump stocks now were within its regulatory definition of machinegun.
The analysis may be useful when civilian courts deal with this issue.