I'm not sure this definition would even apply to bump stocks. The defining feature of an automatic weapon is that it fires more than one round with a single pull of the trigger. A bump stock does not simulate this - no matter what you do it still fires just one round per pull of the trigger. If you say the definition applies to anything that makes the gun fire faster then it would include a lighter trigger or even a fore grip.
Sheesh, someone call Jerry Miculek AND WARN HIM THEY COMING TO “CONFISCATE” HIS FINGER !!