Alright, I gotta jump in here.
On the misconception that a shotgun has a wide spread when it comes to it's pattern. A typical 18" cylinder bore (the bore that will produce the widest pattern) 12ga using 00 buckshot will have an average spread of 8"-10" at 25 yards. The closer the range, the tigher the pattern. What that implies is that a shotgun is not just a "point-n-shoot" kind of weapon. You definately need to train and know your weapon.
It was mentioned earlier that it might be a good idea to use a slug for home defense. I admit that if you hit the bad guy it will be more than enough to stop him. The operative word there is
if. In stressful, panic, life and death situations you might not be able to make sure you have the time to aim properly there by reducing your chances of a hit. OK, now you missed but managed to scare him off or hit him with a second shot. Great. Oops, that missed shot went into your neighbors house and killed a 5yo kid. Guess who is now in deep trouble? Slugs are not appropriate for home defense unless you live in the middle of nowhere and live alone IMO. Too much liabilty.
As to wanting to not kill an intruder, if you shoot him, you better hope he dies. If not, be prepared to have a lawsuit brought against you that more than likely the scum bag will win. If you don't believe me, do the research. You will find many instances where this very thing happened when the perp lived. Sad but true.
Also, pump shotguns tend to me more reliable than their auto counterparts for reasons already mentioned (ammo versatility). I would recommend a Remington 870 or a Mossberg 500. They are two of the best shotguns out there and both have huge aftermarket support.
To the OP, if you are really serious about learning more, check out and read the info on the following sites as they give a wealth of info that is scientific and/or just practical:
http://www.firearmstactical.com/
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