Interested in this as well. I just talked to a FFL dealer and he said that they are only considered illegal if they have a hole in them?
BATFE considers a single part of a suppressor to be a suppressor by itself (with a couple of exceptions like the barrel mount or a non-wiped endcap that changes the diameter of the exit hole).
The solvent traps usually have baffles in them or have a monocore unit that acts as a baffle. Those baffles or a monocore unit ARE parts of a suppressor.
That is why some solvent traps require you to also drill the baffles. By not providing drilled baffles it was a way for the manufacturer to try to end-run around the law. However, they are still considered suppressor parts.
I strongly encourage anyone with a solvent trap to rid themselves of it. Remember, if you pass away unexpectedly your family who inherits your stuff now are responsible for owning an unregistered suppressor. You knowingly made the decision to own it. They did not. Don't put that legal quagmire on them. Just get rid of it.
If you want a suppressor go do a e-file and buy one.
So far the BATFE, to the best of my knowledge, has only prosecuted those who have drilled their solvent traps. They have been collecting the traps nationwide based off of manufacturer, distributor and payment records.
I may be mistaken about the prosecutions because I dont closely follow all national prosecution cases.
If you think buying a suppressor is too expensive, I encourage you to check out the price per hour of the NFA knowledgable and experienced attorney you will need to hire to defend you against a federal felony charge for having an unregistered NFA device. I believe you will find it much less expensive to just buy the suppressor legally.
Not to mention if they get a conviction you will carry that felony for life...which also means no firearms for you. Your deer season will be limited to archery equipment only.
Just my opinions, not legal advice.