Reference this thread for some of the questions brought up:
This thread is my input based on my training and experience, and is not gospel.
Home defense. First, to answer the question of all questions. What is better for home defense?
3. AR15 (or other assault rifle)
The answer, hands down, is the rifle. Why?
1. First and foremost, magazine capacity. People will say, but you only need one shot to kill an intruder. Nice, but how many for a firefight. You grab your rifle, walk into your living room and an intruder unloads on you with a gun. Your natural reaction can easily have you duck and unload a lot of UNAIMED rounds. And the more rounds you fire (as proven in a police study) the less likely anyone will get shot in the gunfight. Never plan on a one shot stop, especially if the intruder is armed. Thirty rounds can go by fast, 15 faster, and 8 even quicker. Not that spraying bullets in a house is a good idea, but it may be life or death.
2. Second, it is the easiest weapon to engage a target with. It has less recoil than a shotgun, and FAR more accurate than a pistol. Go to the range, put a target up at whatever range you deem realistic for a house gunfight. Unload on the target as fast as you can fire accurately hit it with your pistol, rifle, and shotgun. Which gun is the easiest to do it with and has the smallest group? For most shooters, the rifle is the best bet. Trained police officers have missed targets at less then eight feet with a pistol during gunfights... that's with stress and light conditions.
3. People may talk about penetration, but Old_Painless had some interesting experiments (not NASA, but effective) that show that pistol bullets and shotguns will definitely penetrate sheetrock. High velocity rifle rounds fragment and deflect much more readily. Either way, it sucks. Bullets will fly farther then you want them, regardless of the platform. No clear winner here.
4. Pistols are more compact, and shotguns have the racking sound of death. Other than that, be trained on the weapon you choose... and choose the rifle!
Techniques/tactics for clearing a house.
1. Unless a life of an innocent is threatened, don't look for trouble. If there is a hint of a threat, blast that guy.
2. When you have to go on the offensive, be familiar with firing while moving. You may be the master at the Pie, but don't expect the intruder to be a tactical wizz. He may just pop out on you when you are moving between cover, or in a hallway. Fast and accurate wins.
3. If the intruder is in a room, with nobody else and you have no reason to go in after him, just wait him out. Entering and clearing is a job for a team, one guy will probably get shot.
4. If you have to enter and clear a room, enter and break either left or right, GET OUT OF THE DOOR, or as it is called, the Fatal Funnel. That is where the intruder will have his weapon trained.
5. How many times do you shoot someone? Until they are not a threat.
6. Don't challenge a guy with FREEZE or STOP or DROP YOUR WEAPON! According to Ayoob, criminals typically respond to that with a gunshot. If they have a weapon, they are a threat to you and your family. Drop them.
7. Remember the difference between cover and concealment. Concealment keeps you hidden. Cover stops bullets. Most houses don't have much cover. Doors, walls, etc. are NOT cover.
8. Be familiar with some CQB techniques with a rifle. A good sling can help weapon retention. Here are two techinques if a guy grabs your weapon. If you lead around a corner with your rifle (flagging due to space constraints) and the intruder grabs your weapon, step back sharply and smack his hands on the wall. Or, if an intruder grabs your weapon and wrestles the muzzle away from him step back while holding the weapon (sling helps). Unless the guy is Hulk Hogan, as you pull the weapon away, the muzzle is going to point at him no matter how hard he tries. Then shoot him. Try it with a buddy. Sling your UNLOADED weapon, have him grab it, and step back. See if he can avoid the muzzle.
9. Worry about your life first, legal issues second. Better judged by twelve than carried by six. It wouldn't hurt to prepare ahead of time with research and knowing the law. The AR15 is actually a good weapon for court. "Your honor, its what the local police use." So much for it being evil. Ayoob also reccomends you use the same ammo the the local LEOs use for any self defense weapon, just for that reason.
10. TARGET IDENTIFICATION! Don't shoot a loved one. Know where your bullets are going. Put a light on your gun. ALWAYS ID YOUR TARGET!
11. In any incident that you have to even pull out a gun, call the police. If others report it, but you don't, it will hurt your legal status.
Disclaimer: I have never had an intruder in my house. My shooting experience is some IDPA, IPSC, 3-gun, and lots of military as an Infantry officer. I am currently teaching Afghani National Civil Order Police tactics in Kabul.