True story,
Back in the early 80's, there was this company that sold them via mail order (no internet yet) to anyone, anywhere.
A couple guys had bought them in Hawaii.
ATF had come down on this company and confiscated all of their records.
Next thing you know, the long arm of the law came calling.
The people here where asked to surrender the silencers, which they did, peacefully.
Nothing really came of it. They where really after the company.
Things where a lot looser then, but still.
Saw "Shooter", I think he used an empty plastic soda container.