That's true and for a long time the ATF was very unreasonable about that issue.
Now, it seems, they have backed off and only consider "constructive possesion" if the restricted device is the only possible build.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.