Obligatory: I'm not a lawyer, and am also fucking stupid. You would be stupid to listen to me at all.
Apparently, the new hotness here in NY is a non-everything gun: pistol brace, barrel length of 16" or more, OAL w/ brace removed greater than 26", vertical foregrip, built from a 4473-transferred lower. So stuff like this rolling garbagecan/Trijicon advertisement is legal:
The dumpster fire above has a 10/30-round magazine, which is actually of dubious legality.
For the ATF:
--Pistol brace so it's not a rifle
--Vertical foregrip (groan) so it's not a handgun
--26" length with the brace removed so it's not an AOW (some places are reporting "with the brace fully extended", other places are reporting "no, the ATF decided that didn't count"
For NYS, referring to Section 265 of the Penal Code:
--It's not a rifle, because
*Receiver transferred as a receiver, not a rifle
*Brace means it is not designed to be fired from the shoulder
--It's not a firearm, because the barrel is over 16"
The SAFE Act enumerates stuff you can't have on a semiautomatic, detachable magazine-fed rifle or pistol. But here you're in a spot where you don't meet the NYS definition of a rifle, nor the ATF definition of a pistol, and you're not afoul of the NFA.
Unfortunately, the term "pistol" is not defined in the law. My non-scholarly inclination is that that is a fight the state would not want to have, because they've historically tried
really hard for there to not be any rulings on the various grey areas of the SAFE Act.
Also warning that this involves trying to glue together "Shit The ATF Says" with NYS law, along with everything that entails. Gluing them together doesn't always work (why should NYS accept the ATF's definition when they haven't made their own?). The ATF routinely decides to change its mind about shit it says, the shit it says is not law, and even if you're walking around with a copy of the shit they told you, I can think of at least one instance where a judge didn't allow that to be entered into evidence. And of course, it also hinges on NYS accepting the ATF's decision that pistol braces are not stocks.
I'm going to wait and see what happens to the dudes that have built these things, although I suspect it's just going to be a long period of "only illegal when we decide it is".