Quote History Quoted:
Did the seller break the law then by selling it as a receiver?
View Quote
Did he have knowledge that it had been a rifle to begin with, if so, he should have disclosed it, when I sell parts like lower receivers, I always disclose what it began life as, the lower receiver is the part that is covered under the BATF requirements, it is considered the firearm. What type of firearm is determine by the records of the manufacture, as you have stated you know it to be a receiver that began life as a rifle, then you would be in violation if you built it into a pistol.
If the seller misrepresented the lower, then he could be hit, but that would be up to the investigator to determine how much of a prick he/she wanted to be and what the intent was. Got to remember, the BATF determines intent, not your nor the seller. If for some reason a trace was done on that receiver, saying I didn't know would not make a difference.
If it were me, I would build it into another rifle and pick up another stripped lower receiver to build into a pistol.