Just for the sake of discussion on the HD Shotgun vs. Rifle debate, Remington offers a little-known product that attempts to combine the beneficial aspects of both: the
7615 Police.
It's a .223 pump rifle that takes AR mags. Notably, it has a 16-1/2" barrel (shorter than the nominal non-NFA shotgun minimum), and is available with collapsible or short-LOP stocks to minimize overall length.
http://www.remingtonle.com/rifles/7615.htm
I'd argue that it's still inferior to a semi-auto rifle due to the need to manipulate the slide, and I don't think it's quite as short as a 16"bbl AR carbine, but it's a decent choice for folks who want a .223 HD rifle but live in a restrictive state or don't want to project an "Evil Black Rifle" image for whatever reason. I surmise that- with the mag out- most non-shooters won't be able to tell this rifle apart from an old-school riot shotgun.