This is where we get to use bad case law against them. The Kelo v. New London case said that public use including just getting an economic benefit for the community from the seizure. The purpose of this taking is to reduce crime, which is an economic benefit to the community.
So, if I have to turn in my bumpstock or go to jail, it is a seizure. The purpose of the seizure is to gain an economic benefit for the community by reducing crime. This means I have to be paid for it under the Fifth Amendment.
Or they can overturn the New London decision, which would also be a good thing.