Okay, here’s what the ATF decided was a Short Barreled Rifle (SBR), as opposed to an AR pistol with an arm brace.
Why?
No one really knows because the ATF isn’t saying how they decided this. Kind of like the Turks in the Constantinople song.

I don’t know how many of our readers are cognizant of the all the ins-and-outs of pistols and arm braces, but to me I can’t figure out how ATF rationally can call this an SBR without calling every other arm braced pistol/firearm a short barreled rifle, or – like the Mossberg Shockwaves – a short barreled shotgun. Of course, they have ping-ponged themselves a number of times on the subject already, so I shouldn’t be surprised they’ve apparently done it again.

Now does anyone still question about why I refer to them as: BUREAUCRAPS!