I did a search and didn't find very current threads on these two questions.
I'm considering the CZ Scorpion Evo pistol. I would like to add a folding arm brace of some flavor, but am unclear on the legality of the following two points:
1) Did the ATF TRULY give consent to shouldering arm braces, as inefficient as that may prove to be in providing any added stability? I find the verbage of their so-called 'reversal' decision very slippery.
2) If you add a folding arm brace, are you required to meet 922(r) compliance first? I don't see how it would qualify as any of the enumerated parts.
The eventual goal would be to form 1 the thing and get it good with 922(r) regs, but is the above lawful. Naturally the rule of "don't trust anyone on the internet" applies, but is anyone aware of a decision letter on question 2, or strong clarification of the decision letter referenced in 1?
ATF said incidental shouldering is fine.
I take that as, if it brushes up against your shoulder when you are shooting, is probably somewhat unavoidable and they won't be following you home and shooting your dogs.
Intentional shouldering and it would be considered an SBR. Also, ATF has furthered that and said if it has a "more than 13.5" length of pull, they don't like that either according to one of the manufacturers of the various brace companies.
So, if your plan is to throw on a pistol brace and shoot it from the shoulder to bypass NFA laws, my advice is "don't".
To answer your other question, 922 isn't required to install a pistol stabilizing brace because you're not changing anything.
SBR rules for 922 does apply.