Passing a law which you can challenge in court that says “machine guns are illegal now, turn them in so we can melt them down for scrap” is not public use.
The EO couldn't have forced an uncompensated surrender of a registered bump stock, were it one existed before the Hughes Amendment.
There’s plenty of flexibility in the case law for what counts as “public use”, but nearly all of it is about individual cases where the government takes a specific person’s specific property, or damages it in some way. There doesn’t appear to be much case law at all for the guardrails if the government declares an object to be illegal to possess writ large for safety purposes and requires owners to destroy or surrender those objects.
I’m not saying there’s no path where the courts would require compensation, but for the level of certainty you’re claiming, I’d expect there to be a more clear line you can draw to existing cases.
My initial claim in any case was that the constitution requires the compensation, not that there is 0% chance the government would violate the constitution.
None of the above has anything to do with the government violating the constitution.