To make this even more baffling....
I have an AR pistol with full stock. 10 inch barrel. It's not an SBR. Why? It's smooth bore barrel. A rifle with no rifling is not a rifle. Like how a donut with no hole is a Danish. No kidding. I personally verified this with the ATF. It's a Franklin Armory Reformation.
One might say, What hath God wrought? It's a short-distance weapon. The bullets, due to lack of the spin invoked by rifling start to tumble at 20 yards. But with a little practice, you can land every round within the 7 ring of a B27 target at 50 yards reliably. The fact that the bullets are tumbling at that distance literally shreds the target. Some go in point or butt first, others sideways.
The bottom line is that the bad guy standing in front of this beast would look like my mother's meatloaf after 15 rounds. Not a pretty sight. The meatloaf, I mean. I used to call it "roadkill".
The poor guy at my LGS was so befuddled and worried about losing his FFL license by making a mistake or being fined $10k, he asked me to speak to an ATF agent on the phone. I did, then hung up and faxed the agent the info Franklin gave me. I came back the next day and the transfer had been approved. No yelling, no threatening, no vitriol about the 2A or starting an anti-gubbament uprising. It was all very polite and professional on both sides of the issue.
This story and the gun highlight the idiocy of the NFA regarding SBRs.