Originally Posted by veamon
As anyone used one of those oil can converters? I don't know the legality of them, and they're a little fugly, but they seem like a legal alternative that's cheap.
If you're talking about the "solvent traps" that don't require paperwork, the sale of those is dubiously legal just like Spats said. But it's definitely NOT dubious if you're caught using an unregistered "solvent trap" as a silencer; that's a potential ten year prison term and a $250,000 fine.
Originally Posted by Garycw
For the oil filter type you need a tax stamp for the adapter that fits between filter & barrel.
Not only do you need a tax stamp for the adapter just like it was a normal silencer, but you're not even allowed to change out the oil filters yourself; not unless you want to commit a federal felony.
The BATFE regulates what it considers "silencer parts"; when you attach an oil filter to an adapter the filter becomes a silencer part. And just as it's illegal for the user to change out the baffles on a normal suppressor, if you change out the oil filter on an oil filter suppressor you're breaking federal law and you're eligible for 10 years in federal prison and a $250,000 fine. The only way you can legally change the filter is to send the whole thing back to the manufacturer or another properly licensed company.
The adapter is supposed to come with one filter that's serialized, and when that filter wears out you need to send the whole thing back to the manufacturer for them to change the filter for you. Most manufacturers only charge about $25 for this.