I'd use a factory load that duplicates what your local LE uses.
I haven't seen shotguns near as much as the M4's that they all seem to have now. Less mess than SG, more capacity, lighter recoil...223 seems like a reasonable alternative to the 12 ga SG for HD. I have both actually.
My SG is ready too, right beside the AR. I keep my SG cruiser ready with #00-00-slug-slug-slug-slug. The idea being that if two rounds of 00 Buck doesn't stop the threat, then slugs to follow makes all sorts of sense...
Or does it when I could have picked up the AR?