If your desire is to minimize wall penetration then buy a shotgun and load it with bird shot.
Now what did I just say?
Birdshot might minimize the problem, but it'll still go through at least one wall just fine (and maybe more):
http://www.youtube.com/watch?v=0HlNiUpTkLU
http://www.youtube.com/watch?v=xgqbdVFxlkk
Forgive me if I don't address everyone specifically. I am reading all of the posts and find them very insightful. I purchased a box of Hornady XTP 180 gr. JHP when I paid for the gun simply because I figured having some HD ammo was better than none.
There are better these days, but it'll do.
I was impressed with the reviews I found of the Ranger T-Series.
These are not quite as consistent in terms of expansion as HSTs and Gold Dots, but they're still good in that regard and the razor-sharp "talons" that they sprout are nasty!
In my 12 ga. I have reduced recoil 00 buck and, as a last resort, slugs. My set up for that is 4 shells of 00 buck and 2 slugs. I figure if the 4 00 bucks don't take him down, then I need something heavier. I went with the low recoil for 2 reasons. Primary reason being to make it easier for the wife to handle if she were to ever need to shoot the 12 ga. Second is, and I could be wrong in this assumption, that the pellets would penetrate less through walls if they miss bad guy.
#00 buck will penetrate every interior wall of your house, reduced-recoil or otherwise. That's a good load, though, as full 12-gauge power is arguably overkill for human targets anyway (with buckshot). You could also try #4 buck, which is somewhat less penetrative than #00 buck but even more devastating to bad guys (27 pellets penetrating a foot deep will do that).
As for the mixed load, it's really only an advantage if there's a good chance that your target would be wearing body armor, I suppose. It's usually better to know exactly what you're going to shoot with every pull of the trigger, and to make it the most effective load, which slugs, against unarmored targets, are not--buckshot is what really stops assailants cold. Also keep in mind that it is common for there to be more than one assailant in a home invasion.
In the various reviews of JHP rounds I've read, the expansion of the round is always pointed out. How critical is it to have "the" round that expands the most? I guess what I'm really asking is, do I lose much effectiveness in a JHP round if it isn't the one that expands the most?
Many people do seem somewhat obsessed with expansion because there have been so many developments in that area, and new technology is always a big draw. What I'd suggest, as mentioned earlier, is to decide how much penetration you want, and then choose a round that gets at least that much penetration and the most expansion among those. For the most part, just about any .40 S&W JHP will do for most people (except maybe for that weak 135 grain Homeland Security load that Winchester designed to their specifications, although it certainly can still kill).
It gets much scorn, but another gun I think might just be the answer to dry wall concerns is the Judge loaded with number 4 lead shot loads. Shoot for the face. It'll be close range. Maybe back 3 rounds up with 000 buck loads.
Go ahead and bash me for my opinion, but it makes sense to me. I don't own a Judge, don't live in apartments.
Well, if there are any special purposes for this gun, then this might be one of them. I wouldn't recommend this tactic, but it's a personal decision. You could also load a regular pistol with pistol-caliber shotshells from CCI for face shots, backed up by JHP rounds.
Also, can someone explain the relevance of the inches of penetration as it pertains to actual penetration into a bad guy? I read the 12" standard for the FBI above and was curious about it seeing as how most people aren't 12" thick... Forgive my ignorance in this respect but I haven't quite understood the direct correlation. Thank you again.
The FBI actually recommends 12"-18" as a useful range (with 18" being preferable to less, and more being overkill), based on studying their collective experiences in shootings (and probably other data as well). This recommendation tries to take into account shots from angles at which the human body presents a much thicker target than usual, as well as the fact that bullets may have to penetrate limbs and even bones to reach vital tissues. The latter is a reason that I personally prefer heavy-for-caliber bullets with high sectional density and momentum, as they tend to be better at penetrating bone (or other hard barriers) as well as staying on target in doing so. In my opinion and that of the FBI, as it happens, 12" is really a bare minimum, but even so, a lot of people don't even attempt to better it.
The reason you want a projectile to penetrate at least 12", is that most people aren't 12" thick. You WANT that bullet to do damage from one side of him to the other, with as big of a wound channel as possible. A good shot that would hit the spine won't do much good if it doesn't have enough energy to reach it. The further it penetrates, the higher the likelihood it will hit something that will make the bad guy stop what he is doing. I don't want it stopping halfway. I want a premium hollowpoint to mushroom to at least 1.5 times the diameter of the projectile and go all the way through. I want as many pellets of buckshot to tear all the way through him creating multiple wound paths. The more wound paths, the greater the chance of incapacitation. Not complicated.
The load that I currently use approaches 15" of penetration in bare ballistic gelatin and far exceeds that--sometimes over 19"--when passing through clothing first, giving up some expansion in the process (maybe the FBI and I do think alike after all in selecting the very same load, which was in fact developed specifically for them). It's up to me to ensure that my chosen defensive load will be effective when I need it, and I don't want to end up dead just because the target was too obese or the angle was oblique and an otherwise well-placed bullet simply failed to penetrate deeply enough. :banghead: Here's the bottom line that is potentially true for each and every shot that I may have to take in self-defense: if it's human, then I can kill it.
and comments 
from visitors when they notice that you've nailed the sofa, lamps and coffee table up on your living room walls.
