Is there ever a time it can be shot from the shoulder legally?
Once you SBR it.
The only reason I almost got an AR pistol was because of the Sigbrace being a great way to shoulder fire. Now that the ATF has put the nix on that, I’ve lost interest. SBR is the only way to go.
My understanding is that the ATF is still of with “shouldering” a pistol buffer tube, as long as it doesn’t have a Sigbrace, Shockwave brace, etc attached to it.