I guess the Marines kicking doors in Fallujah should trade up to handguns with birdshot.
I generally stay out of tactical discussions because of my lack of experience, but I'll jump in this time on the basis of witnessing 5,000+ room clearings. Active LEO's carry what they're issued, but those that can choose overwhelmingly go with a shotgun loaded with slugs. In most cases these guys are ex military and contractors, or LEO's on leave of absence, vacation, or some sort of time off.
They go with slugs to stop the fight and precisely FOR the reason they can shoot though interior barriers - walls, a mattress, a couch, or whatever a bad guy will use for cover. There are shared horror stories of having birdshot from a riot gun bounce off room décor while the bad guy opens up with a double stack 9mm.
These same guys prefer a M4-type weapon for the open streets, and many will carry both a slung shotgun with slugs AND an M4 and switch from one to the other moving from street to buildings.
