@Dave686,
You’re right about the disability part. I get it now.
Does the BATF define what “shouldering” means?
Without a definition what is a “cheek rest”? A accessory or a shooting stance?
I don’t pretend to be an expert on this ruling, and I didn’t sleep in a Holiday Inn last night.

But I have read it, and if you are looking for some way around this without registering your SBR, I don’t see one. It’s obvious to me people who are knowledgeable on the AR and this application have been involved in writing this and covered all bases.
I don’t see how you use it matters as much as the gun itself. Throughout the document they talk about Shoulder fired and definitions and intent, and the mistakes and assumptions they made.
This might help you.....
Accordingly, the Department amends the definition of ‘‘rifle’’ under 27 CFR 478.11 and 479.11 to expressly state that the term ‘‘designed or redesigned, made or remade, and intended to be fired from the shoulder’’ includes a weapon that is equipped with an accessory, component, or other rearward
attachment (e.g., a ‘‘stabilizing brace’’) that provides surface area that allows the weapon to be fired from the shoulder, provided other factors, as listed in the amended regulations and described in this preamble, indicate that the weapon is designed, made, and intended to be fired from the shoulder.
The other factors are:
(1) Whether the weapon has a weight or length consistent with the weight or length of similarly designed rifles;
(2) Whether the weapon has a length of pull, measured from the center of the trigger to the center of the shoulder stock or other rearward accessory, component or attachment (including an adjustable or telescoping attachment with the ability to lock into various positions along a buffer tube, receiver extension, or other attachment method), that is consistent with similarly designed rifles;
(3) Whether the weapon is equipped with sights or a scope with eye relief that require the weapon to be fired from the shoulder in order to be used as designed;
(4) Whether the surface area that allows the weapon to be fired from the shoulder is created by a buffer tube, receiver extension, or any other accessory, component, or other rearward attachment that is necessary for the cycle of operations;
(5) The manufacturer’s direct and indirect marketing and promotional materials indicating the intended use of the weapon; and
(6) Information demonstrating the likely use of the weapon in the general community.
All of the objective design features and factors listed in the rule that indicate the weapon is designed, made, and intended to be fired from the shoulder are derived from the NPRM and proposed Worksheet 4999. The revised definition in this final rule clarifies, consistent with the best interpretation of the statutory provision, that firearms with an attached ‘‘stabilizing brace’’ can possess objective design features that make them ‘‘rifles,’’ as that term is defined under the NFA and GCA. If a firearm with an attached ‘‘stabilizing brace’’ meets the definition of a ‘‘rifle’’ based on the factors indicated in this final rule, then that firearm could also be a short-barreled rifle depending on the length of the attached barrel, thus subjecting it to additional requirements under the NFA and GCA. However, a firearm with an attached ‘‘brace’’ device is not a ‘‘rifle’’ as defined in the relevant statutes if the weapon is not designed, made, and intended to be fired from the shoulder. The rule, as proposed and finalized, does not ban ‘‘stabilizing braces’’ or prohibit firearms with an attached ‘‘stabilizing brace,’’ regardless of the firearm’s classification. This revised definition reflects the Department’s understanding of the best interpretation of the statute, and it is immediately effective.