Home Defense for Everyone
As much as I like fully custom ARs and red-dot sighted handguns, these are not the best tools for people to start with. Assuming someone is getting into firearms to protect their home, but isn't sold on the concept of gun culture or collecting guns for various uses. We'll assume this hypothetical buyer only intends to buy one gun, doesn't want to spend more then ~$500 and needs effective stopping power. They aren't going to do any modifications that require more then turning a screwdriver, and won't spend a lot of money on accessories. The gun has to be light and low recoiling, so that people with disabilities can effectively use it. It would be best if the gun had a light trigger pull and operating force for the same reason. i recommend long rifles over handguns because it is easier to learn and make accurate hits with a rifle. Concealment is not a primary concern, but we will have a handgun section too.
Long Guns:
My first recommendation would be pistol caliber lever action rifles from Rossi or Marlin with the shortest barrels available. In 357 or 45 Colt, the recoil would be light, stopping power would be acceptable, handling is not too difficult and the gun would be small and light enough for just about any user. These guns have MSRPs around $500, and their ammo is easy to find. I'd generally recommend that a red dot sight be mounted and zeroed for ease of use, and perhaps a flashlight clamped to the barrels.
Alternatively, a 410 pump action shotgun with an 18" cylinder bore barrel loaded with slugs would be almost as good. The ammunition is more expensive and capacity is lessened. Purchased new, you'd need a Mossberg pistol grip 410 and a standard butstock to swap on, there are no current factory guns in this configuration that I can find. There may be used guns on the market that fit this bill as well. Like the rifle I'd recommend a red dot sight and a flashlight clamped to the barrel.
Historically the M1 Carbine was the go-to rifle for this, and I really wish that it was still inexpensive and reliable. But with magazine issues and prices climbing as collectors eat up the market, I can't recommend it generally. However, the M1 Carbine's design is the gold standard for this idea.
In other states, used Marlin Camp Carbines and Ruger PC9s and PC4s would also excel for this concept, if they can be had in the right price range. The Timberwolf pump action 357 and no longer made Winchester pistol caliber lever action rifles are other used guns to keep an eye out for. As for new guns outside of California the Keltec Sub2000 or even the HiPoint carbine would both be reasonable choices. Both of which would require modifications in California for legal reasons. All would benefit from a red dot sight.
Sub optimal choices are much more common. Sacrificing light weight and low recoil, 12 and 20 gauge pump shotguns are the traditional answer to this question. But they can be intimidating to new shooters and difficult to learn well. If they are chosen, I'd suggest buckshot and while a light is always a good idea, the red dot probably isn't as needed. On the other side of the spectrum, sacrificing stopping power for light weight and low recoil, 22 Long Rifle semiautomatic rifles would be better then harsh language. Here I would stress the importance of the red dot sight and assuming a failure to stop, requiring multiple hits. The Ruger 10/22 would probably be the best choice of these guns, and I would also recommend the aftermarket magazines that are not rotary, to allow more purchase when removing them from the gun and loading a replacement.
Handguns:
For some people a home defense handgun might be a easier solution. Handguns are easier to conceal in the home, deterring theft and misuse. They can be packed into small, unobtrusive locking cases, making sure your neighbors don't know that you have a gun when you take trips to the range. The can also be carried concealed where legal or appropriate.
If you live in a part of the country where used firearms are more common, used Glocks, regardless of caliber (but with a preference for 9mm) are your best bet. They are inexpensive (typically selling for around $400), reliable and spare parts and magazines are both plentiful and inexpensive. Alternately, the full sized grip, 3+ inch barrel 357 magnum exposed hammer revolver is another good solution. Both of these are widely available used in states with decent used gun markets. Make sure the grip fits you and you can reach the trigger, hammer andb other controls.
In California I recommend the Kahr CW9. Its not perfect, the slide is a little stiff, the grip is a little thin, but it seems to be easily accessible to every hand size. the Sig SP2022 and sometimes Springfield XDs fall into the price range as well. All are quality guns I would trust with my life.
Finding an inexpensive revolver in California that I can recommend is difficult. The Charter Arms revolvers with a full sized grip would be acceptable, if not ideal, due to their short barrel lengths. In the tradeoff category, any decent semiauto 22 Long Rifle pistol would be better then nothing and would be easier for people with hand strength disabilities to work with.
Avoid 380 and 32 ACP pocket pistols and any gun where you can't fit your whole hand on the grip. These sacrifice usability for conceablity and often lack the stopping power desired for self defense. Alternately, avoid 45 ACP in favor of 40S&W and 9mm. The difference is not worth the recoil. For all handguns I recommend some sort of holster, just to make controlling the handguns when not in use easier, extra magazines or speedloaders, and as much ammunition as one can afford. If the gun has a rail for a light (like the SP2022, Glock or Springfield XD), this is definitely an upgrade to invest in.
