The problem, as I understand it, is for a modern firearm with a bore over 1/2 inch to not be defined as a destructive device. It must be either a shotgun or a rifle.
The definition of a shotgun states it’s shoulder fired.
So pistol gripped shotguns, except 410’s, are now destructive devices.
That's what I'm getting out of these recent articles but that is contrary to the statutes you posted. I'm beginning to think that both the ATF and the NRA are deliberately confusing the issue.