Swede, as to how much ammunition to have on hand, I prefer to have a couple boxes (20 rounds) of several sizes. Birdshot in #6, buck, #2, t-shot, and slugs.
I figure 100 rounds are enough to either get you in trouble, or get you out of it.
If you are looking for a purely defensive weapon, a 12 gage riot gun with a folding stock loaded with #2 or #4 shot is very persuasive as it will do a lot of damage at close range on a thin skinned /light boned opponent like a human. These come with an open choke for maximum spread at close range.
To those who are not really familiar with firearms, a riot gun is so called because it is the heavy weapon issued to police officers. It is not made for hunting or survival, it is a purely defensive weapon. Short barrel, usually with a pistol grip,(a folding stock will help control recoil), usually carry 5 rounds in the magazine.
Kentucky Bob is correct about chokes, but his discussion is geared toward hunting weapons. Self defense is more about getting a hit on a target. Patterning is great for turkey hunting, or waterfowl where you are shooting up to 40 yards, but when the range is measured in feet, the term "spray and pray" comes in.
In the point blank range of fighting in the confines of a living room, patterning is not as important as it is at distance. When you are only shooting a maximum of 20 feet, that is only 6 yards, and most rooms aren't that big.
A shotgun you can hunt with has a longer barrel, full stock, more accurate and versatile than a riot gun. I classify them in a different category. They fire the same rounds, using the same mechanisms and physics, but a hunting or sporting weapon is harder to handle in close situations.
While I am a huge proponent of being used to the weapon, and practice, I would rather have something that anyone who is in danger could fire with a better than average chance of dissuading an attacker.
Pistols are fine as a weapon. They are convenient, fast shooting, acceptably accurate, but they need a lot of practice to use efficiently.
I do have an experts medal for handguns, but I would never choose it for situations where the target is uncertain such as in bad light. One problem with popular Semi auto handguns is that it is easy to fire several rounds quickly, whether you want to or not. I have seen people fire the first round into the target and the next 2 into the sky.
It takes a lot of practice to use a handgun efficiently.
A revolver is easier as you have to make a serious effort to pull the trigger in double action, or cock the hammer each shot in a single action mode. They are usually more accurate than a semi-auto, and chambered for heavier rounds. They are more versatile as a hunting weapon and can be a very serious weapon.
However, that power translates into collateral damage when the round passes through or misses the target in a close fight.
Rifles are superb for hunting. Accurate, come in all calibers for all occasions. However, they are hard to maneuver in close situations. They are longer, and it can take time to load if you have a bolt action. Lever actions are shorter, faster to handle, good knock down power, but not something I would want to try to defend myself with at 2:00 AM.
You use what you have, but in a purely defensive situation at point blank range, a riot gun, no choke, will blow big holes in your attacker. A pistol round will not knock down an attacker unless you hit a major bone as the round will pass through and leave a small hole with some damage. You need precision to hit vital areas like the heart or brain.
A rifle at close range is worse as the bullet won't have time to expand properly. They are designed to penetrate heavier animal mass and mushroom to transfer kinetic energy into the target in the form of Hydrostatic shock causing organ damage and possibly stopping the heart through shock alone.
A shotgun will make BIG holes in the target
You do not have to precisely hit a spot to cause a lot of damage. A shot that hits with only half of its pellets could still take off an arm or leg or damage it where the attacker is effectively removed from the fight.
As this thread is dedicated to people with little or no knowledge of weapons, my baseline is the weapon that is simplest to just pick up and fire with minimal training.
Everyone has preferences with weapons, they are a very personal choice. I do reccomend taking classes for anyone who is thinking of purchasing any weapon for not only their own safety, but for the safety of those you protect.
Survival weapons, hunting weapons, offensive weapons, and firearms for just pleasure shooting are all part of the equation, but if you are just at the level of home defense, a riot gun is hard to beat.
It is hard to absorb all the information available from a few posts,
but this is one of the best tutorials I have ever seen on the subject matter.
Kudos to all the posters.
Thanks especially to Kentucky Bob, that is a lot of writing pal!!
I surrender the soapbox to the next participant.