I would only shoot slugs through the rifled barrel. Extra barrels are fairly easy to find for the 500 in a smooth bore if you are wanting to use some type of shot.
Pump gun
I have a BPS also, and i love it. I think the pump may be the way to go. If you feel that you have a prowler, you can cycle the gun action. That sound is unmistakable! Not something an intruder wants to hear.