attach these photos if you comment. they are recent determinations, etc.
borrowed/stolen from an arfcom post.
also in 2017....
Case No. 3:16-cv-243-RLY-MPB
UNITED STATES DISTRICT COURT SOUTHERN DISTRICT OF INDIANA
On July 27, 2017 DOJ/ATF stated:
"Bump firing is the process of using the recoil of a semiautomatic firearm to fire in rapid succession, simulating the effect of an automatic firearm when performed with a high level of skill and precision by the shooter....The rapid fire sequence in bump firing is contingent on shooter input, rather than mechanical input, and thus can not shoot automatically"
On Sept 13, 2017 DOJ/ATF stated:
"Because of the manual, skill based methods required to operate a bump fire device" they are not machineguns.