Have you ever heard of "constructive possession" and have you considered how that concept would apply to having such a device along with a firearm to which it can be attached?
That's what worries me. Maybe I've got some gun parts in the garage, and maybe a couple of oil filters. That coincidence is innocuous enough.
Add in an adapter that's specifically made to adapt one of those oil cans to one of those guns, and we're in different territory.