Wow... Thanks Aarond. That's well, I think I'll look at the T/C catalog.
What Aarond pointed out is a prime example of what I am asking about. As David mentioned (and can be found on the ATF's website) a receiver sans smooth bore barrel is not a NFA item.
"No, it's not a silencer. This little doodad is my own invention. I call it a loudener." --Sledge Hammer