The adapter is available – HERE (bottom of page)
$55 gets you the adapter which is the part you register with the ATF according to the website. The oil filter is considered the removable expansion chamber.
Pretty cool as a novelty. Unfortunately there doesn’t appear to be any videos on YouTube of people using one of these things.
It’s too bad there wasn’t more specs on how to use it, and noise reduction info on the website.
It would be funny if the same company came out with a set of EXTREME hi-rise sights especially for this application. LOL