Re: SBR Legality Question
Minimum length for a rifle barrel is 16", including any permanently added on muzzle brakes, etc.
Shortening that barrel to any overall length less than 16" will require registration as a SBR. If you do that, and then decide to CHANGE the barrel length (say, 10.5" to 7") you would have to go through the entire registration process again.
The autonomic nervous system provides for involuntary muscle function - the work of breathing, digestion, and so forth. On some folks, that's a pure waste of ingenuity.