If you can’t legally sell something then you don’t actually own it.
In Massachusetts those who own AR15s from prior to July 20 2016 cannot transfer them except out of state. Those who own bumpstocks currently have no recourse to transfer them, in or out of state. Government requires them to be turned in or destroyed (or maybe just turned in, can’t remember what the edict was exactly)— no compensation offered. How’s that fot constitutional?
Case in point, lawn darts. Or a bag of heroin.
Tangential trivia, did you know that the word "heroin" began as a trade name?