"the ATF seems to only regulate the cosmetics, not the end use."
(Yeah, it's Wiki, but whatever)
"Short-barreled rifle (SBR) is a legal designation in the United States, referring to a shoulder-fired, rifled firearm with a barrel length of less than 16 inches (40.6 cm) or overall length of less than 26 inches (66.0 cm)."
IIRC, the law itself refers to a "shoulder fired" arm as well, as opposed to "designed to be fired from the shoulder." That kind of language is what's seen in 922r, which is why spade-gripped belt feds don't need compliance parts. Unlike the more modern laws which really do accomplish nothing but cosmetic restrictions, the writers in 1934 actually had enough sense to more or less ban the activities they wanted gone (concealable rifles, shotguns, sound-reducing features, cheap/simple rapid firing autoloaders) and left enough vagueness for an unrestricted regulator to fill in plenty of gaps. The reason the angled foregrip by Magpul isn't considered a vertical foregrip in the AOW sense, is because it is a shallow enough angle its use is indistinguishable from a truly horizontal grip (yeah, I know, it's an arbitrary distinction, but that's basically what the ATF's finding was)--there's still no defined angle that constitutes "vertical" in their mind, so every different submission must seek independent approval. Part of me wonders if SIG and Magpul get away with these things simply because they do so much government work that the ATF is not sicced on them by hostile authorities.
My beef with people pushing the ATF ("poking the bear" as it were) is that it is ultimately pointless. Unlike a real system of law, where precedent carries real weight and consequence, at the ATF it's basically decided by individual agents at individual times with no regard to the past or future ramifications. I think reproduction Mauser Broomhandle stocks have toggled legal/illegal about a half dozen times at this point. Ergo, all the bravery and sacrifice in the world to "stand up the man" and force the ATF's hand can be undone by the next Bureau head (and will be). It's like trying to force the President to undo his Executive Actions --why bother? They carry no weight to the next guy and will be removed much easier if they remain odious.
What we need is people to contact their reps and make them pass a law requiring A) the ATF to clarify its position in a legally-binding way on a range of common disputes, or B) define new specific guidelines the ATF is to abide by going forward, or C) stipulate that ATF approval/rejection letters are to be considered legally binding, public (after some fixed delay, to protect innovation), and are to be reviewed/approved if not written by a court of judges independent of the agency (and Executive branch, preferably). A) Gives the ATF too much input, B) gives Congress too much input, C) at least forces them to follow the rule of law, which is what's been lacking up to now. It would at least preclude the idiotic "daddy says no, mommy says yes" situations.
Basically the Tech Branch needs to start behaving more like the Patent Office if it aims to classify and regulate every facet of technical gun design, instead of making up ham-fisted judgments based on whimsy as it goes along. Ya'll should read up on the EP Armory/Ares dispute over 80% lowers in the Legal forum as a corollary to this SBR nonsense. The ATF is effectively holding that a block of plastic with no holes drilled is a semi-auto AR15 (which has two holes drilled), but not an M16 (which has three holes drilled). Further, that they're totally cool with an unlicensed business possessing thousands of illegally-manufactured 'firearms' for a few days so long as they are handed over for disposition --but only if customer records are surrendered as well.
TCB
That would get some notice at the local 3-gun match!
