ATF lacks authority to regulate AR15 lowers as firearm receivers, maybe
Joseph Roh hosted "build parties" in which people finished 80 lower receivers on his machine. ATF didn't like that, and sent him a letter asking him to stop. He declined and was charged. Yet, the government dismissed charges that had been pending for five years rather than lose the case. Turns out, the regulation under which the government would be prosecuting was never correctly promulgated, and the statutory definition doesn't describe a lower receiver.