global,
Your options will vary depending on your and your SO's comfort level and budget. Good options include:
M1 Carbine loaded with expanding rounds;
.223 Carbine loaded with expanding rounds;
20 or 12 gauge pump or semi-auto (if your SO is willing to practice)
20 or 12 gauge double
If you choose a shotgun, please don't load it with birdshot. Also, please don't think .410 birdshot is good for anything other than experts shooting birds. I personally use reduced recoil slugs for defensive use, when using a shotgun (but prefer a .223 carbine). DON'T accept the opinion of random people on the internet about what actually will happen once a round hits flesh. Instead, take the few minutes of time it will take to actually research this on the net. Use search terms like "terminal ballistics" and "ballistic gelatin". Remember that penetration in gelatin will exceed penetration in tissue by at least a little.
It's not a bad idea to actually take ammunition that you can afford, which is dependable and accurate in your firearm, and test it out something. Water will tend to give deeper penetration and greater expansion than flesh, but you should be able to get an idea of what your round will do. Personally, I find three milk jugs to be about the penetration I want my defensive rounds to show.
Less effective and tending to penetrate more, any pistol caliber carbine. These do have the advantage of very little recoil.
Something else to consider, is a hunting rifle. Yeah, it will be loud as hell, but I've been present when a .270 went off inside before. Not pleasant, but I wasn't stunned or anything. If you can afford the money for a new firearm, you can probably afford electronic muffs that will allow normal hearing, but cut out when a shot goes off. Good investment. Anyway, if you go the hunting rifle route, choose a light for caliber round. If you chose a nice, lightly recoiling .243, for instance, pick something like a 75 grain VMAX for home defense. If the target is hit, far
fewer worries about overpen than a sturdy handgun round.
But don't take my word for it. Do the research, or invest a few bucks into testing it for yourself.
A sweet, great handling little rifle with low recoil is the CZ 527 in 7.62x39mm. Put a decent little 2x scope on this, and you've got a neat little rifle that can defend the homestead, is fun and inexpensive to shoot at the range, and that can take deer and hogs at reasonable ranges. Quality ammunition is now available for these, but again, all you have to do is invest a little time into testing for yourself. You may find that cheap 7.62x39mm HPs are highly effective and don't overpenetrate.
Good luck and have fun,
John
