Basically everything else can be owned with an NFA tax stamp. Nuclear weapons my understanding is the difficulty is more with laws on handling the material than specifically owning one as a weapon, so I'm unsure those are even outright illegal either.
Explosives are actually one of the ones with looser restrictions. Even felons can own and re-instate their explosives rights, because bafflingly when congress de-funded the firearms rights restoration process for felons they forgot to do the one for explosives. Felons can also own and manufacture explosive black powder without scrutiny or paperwork, even ones intended to go in a black powder gun.
There’s a whole community of folks building semi-automatic auto-return triggers that are “technically” semi automatic, but with just a gentle squeeze, fire off another. If you maintain that grip, the return mechanism engages, returning the trigger to firing position, where your pressure causes it to fire again… it’s called a Forced Reset Trigger.
My point overall was government is fine with arbitrary exceptions that would get Stan's dad going all "Oh I'm sorry, I thought this was America."