In the United States, the proliferation of files from repositories like DEFCAD in 2021 directly forced the hand of the Biden administration and the ATF. This year saw the drafting of new federal rules aiming to redefine what constitutes a "frame or receiver," a direct countermeasure to the widespread adoption of 3D-printed lowers.
Several historic and highly influential file packs reached peak popularity or were cataloged on DEFCAD during this period: defcad files repository 2021