I've never heard of anybody that was pinned down in their living room and needed to lay down supressing fire. I always here people talk about having enough ammo. If you pump 50 rounds into a home invader you'll probably be on trial for manslaughter soon. If your home is being assaulted by a mechanized infantry division, you are screwed mo matter how mufh ammo you can load into your gun easily. When I was selling guns, my recomendation was always a nice bright shiny nickled S&W .357with a 4+.inch barrel and crimson trace grips. Not sexy, but reliable and easy to maintain. If you want a home defense weapon that is also a toy, don't be afraid to admit it. If you are planning for your upcomming appearence on Disaster Preppers, that swings things more to the carbine.
If you have the wife in mind, then a shotgun is out of the question. The recoil on those things are insane. I would go with the rifle if it's only for home protection. Weight, recoil, and the accuracy are hard to beat. The only reason I bought me and my wife a handgun was because of concealed carrying purposes.
Home Invasions go south as soon as gunshots are fired. Not only does it strike fear into the the invaders, but it attracts the attention of surrounding homes. The burglars aren't going to sit there and get into a firefight with you when they know there are probably 3 police cars on the way. However, to be better safe than sorry, a shotgun would be more efficient for these type of situations. Unless the OP lives in a rural area, then I'd suggest an AR as well.
Desert Eagle. Uses a gas-operated mechanism normally found in rifles so you can use more powerful cartridges. Plus it looks cool.
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A full weight 20-gauge should have recoil that is manageable by most people. Load it up with some #3 buck and you are good to go for pretty much any reasonable home defense scenario.
I'd go with a shotgun, but going to the range and trying the guns you are interested in before buying and talking to an expert is probably a better idea than listening to a bunch of Rockets fans that may or may not have any idea what they're talking about. Anybody ever shoot at an intruder in your house or on your property? Did you hit them? What kind of gun were you using?
In all seriousness, I would recommend a Glock 40 cal. Plenty of stopping power, a very smooth shot and very reliable. A carbine is simply too much for home defense. Sure, you can load 50 rounds into it. The idea is to stop a prowler, not turn your living room into a war zone.
I am also in the market for my first gun. My friend just bought a AR 15, along with his all his other guns. Looks bad ass, and I am gonna shoot it soon with him, but is very unpractical. I was thinking along the lines of a glock 40. I have ask random cops when I see them, and alot of them use this gun, must mean that is good for protection, I suppose. My uneducated 2 cents.
If you really wanted to go bat**** psycho, they make a 30 round drum magazine for the Saiga .410. The Saiga is basically a semi-auto AK that has been retooled to be a shotgun.
The worse case scenario, and more practical, is mistakenly shooting an innocent person. Im all for gun rights, but this "worse case scenario" mantra is horrible logic. If someone lives in a bad neighborhood, then yes, its acceptable to have some reasonable firepower. For the majority of the rest of us, a 22 is plenty sufficient to keep the vast majority of threats at bay. If I ever feel like I need some serious firepower for self defense, then its probably time for me to move to a better part of town.