Say Uncle links to an interesting concept for a suppressor that uses an adapter and a simple oil filter.
This is a legal and registered silencer that is patent pending. It is an adapter that uses a disposable expansion chamber aka a car oil filter. You will get hundreds of shots untill it starts to get loud again. Then all you have to do is throw away the used can and thread another on our adapter.
Not something I'd want to try. The ATF isn't known for having any common sense or respect for the rules, and even if they did, they have a tendency to change the rules at will then punish people for their inability to predict the future.
In this discussion, the armchair lawyer brigade is trying to whittle down the actual definition of what makes the suppressor. I find it entertaining as there really isn't a way to logically do so. I could purchase all the parts to make a .50 BMG suppressor, assemble them in a way that could not be physically placed on any known .50 caliber rifle, and still be in violation of the law. My intent is irrelevant, and that is a dangerous, dangerous game we've allowed to play out.
I'm still of the belief that attempting to regulate things rather than setting punishments for specific behavior it idiocy. Things can be created from scratch, and the doohickey the law focuses so intently on can be modified so that my thing doesn't exactly match the definition of the legal thing and therefor isn't really a thing per-se.
Mowing down a bunch of blind orphans on a field trip to the art museum though? That's a behavior that's easy to identify, isolate, and punish for. Trying to decide if the particular paint job or threaded doodad on the firearm wasn't documented properly is not only harder to do, it has no bearing on the action of the individual.
This is why I laugh at the anti-gunners. They are so assured that simply making an object illegal is all it takes to stop a specific behavior from happening. Unfortunately, enough people have such a loose grasp of logic that they've been mislead into thinking that's a great idea.