this maybe a novice question and thats because i dont a lot when it comes to class 3 items. why does a lower receiver have to be stamped for a SBR? i would think the upper would need to be stamped seeing how its what has the shorter barrel on it. again, i apologize if its a stupid question, but this is the best place to ask. oh, and come someone tell where where to go to download/print the paperwork for an SBR?