I have seen some clips on the news where police officers empty their entire pistol into suspect who would not step down. As a guy who is in college who studying criminal justice in hope of one day being a sworn officer of the law I can say that the typical officer isn't going to see a fire fight in his career. Those that do tend to get full of adrenaline and just unload on a guy. Now tell me who you would be more worried about, the hyperactive cop or the hoodlum with a gun.
On the subject of the police, a metro cop can respond anywhere from 30 minutes to 2 hours. A town cop can respond within 30 minutes to 1 hour and a small town cop will be on seen in a heart beat. County Sherriff Deputy can take hours to arrive on seen out in the rural areas, same thing with state police like Highway Patrol and State Troopers. Also in many states local law enforcement agencies are getting their budgets cut, which means you will your specialists layed off and fewer patrolmen on the streets. Not good in a city environment where you are spread thin and need help right away. In my opinion non lethal shotgun projectiles like bean bag rounds and rubber buckshot should be available for civilian ownership as an alternative to buckshot(normal buckshot and lethal ammo should also be sold, but the nonlethal stuff should mostly be sold in big cities). This way people can repel home invaders without killing them. Also long ranged tazers and pepper balls for paint balls should also be sold to civilians, especially in cities where gun control is strong. Currently all these things are only available to police and military.