You were talking about some questions I'd like to discuss briefly. I'm going to stick to mostly technical elements here.
@LEGERdeMAIN made a good point about what an "assault weapon" is. This term is used in a legal context in the United States when referring to weapons covered by the "assault weapons ban". The term is used in popular speech, which refers to civilian variants of military weapons.
You can read a little about the Assault Weapons Ban here:
Keep in mind, the "assault weapons ban" did not ban automatic weapons or "machine guns", those have been (essentially) illegal on a Federal level since the 1930s.
What are some practical reasons why someone would want to own a rifle based on a military weapon?
- Having a rifle that is based on a common variant means parts are common and made by a variety of manufacturers. Ammunition is less expensive and easy to find.
- Military rifles are, as a sweeping generalization, robust and dependable.
- These designs represent "the best" in handling and use.
Let's get into some reasons why they would be desirable for someone particularly interested in a home defensive rifle.
- Variants of the AR-15, popular in the US, tend to have collapsible stocks. This makes the rifle more comfortable to use, but in a home environment can make the rifle shorter, allowing you to move around with greater ease. Relatively light weight rifles also allow you to keep one hand supporting the rifle against your shoulder while you perform critical tasks, like directing children into safe zones, operating door knobs and locks, flipping light switches, and using your cell phone to call the police.
These are also reasons why a handgun is appropriate for a defensive task in a home environment.
A conventional shotgun or hunting rifle is too heavy and too long for this sort of use. Short barreled shotguns may work though they are generally quite heavy.
- They are able to be equipped with items such as lights, sights, lasers, and grips. This might seem unimportant, however, being able to mount a light onto your weapon is, in my opinion, absolutely essential to proper target identification (who/what am I pointing my weapon at?), checking the status of your target (are they armed? are they surrendering?), and if you have to shoot, making sure you know what is behind your target.
I would not understate the value of a light, I truly consider it to be an essential part of a home defense weapon, and while I don't own any guns, I would not buy a defensive weapon that could not be equipped with a light for use in a home environment.
Again, (many) pistols can be mounted with lights, and could also serve this purpose. I don't know of any revolvers that have rails. Some shotguns as well.
In this case, I'd bring you back to my first note - while other weapons could serve this purpose, popular variants of rifles like the AR-15 have enormous aftermarket support that could fit all budgets.
Items like fore-grips may be useful in close quarters, and a laser sight is useful for placing shots on target.
- Low recoil weapons that shoot .223 ammo are (as a generalization) easier to keep on target than something like a shotgun. This is a consideration for people who are smaller, weaker, in poor health, etc. Someone who is older might not be able to operate a shotgun.
- In a similar vein, a rifle with a "pistol grip" is more comfortable to operate than an over hand traditional styled weapon.
- Slings and mounts: while any old rifle can be equipped with a sling, modern styled 'assault weapons' may be easier to mount with something that hangs on the front of your chest, allowing you to use two hands but keep the weapon on the ready.
A quality holster for a pistol can serve a similar purpose, though being able to hang something off your person is easier when you're not wearing a belt already.
- A rifle or carbine can be aimed with much greater accuracy and speed in comparison to a handgun, an important tactical and safety consideration.
- Ammo, penetration, and safety. .223 rounds are high speed and light weight, however, they demonstrate less penetration through construction materials inside a house in comparison to heavy shotgun and handgun loads. This is a serious safety consideration.
(Frangible loads that will 'turn to powder' when they hit hard targets are available, but are a bit of a special case.)
These are some reasons why someone may want to own an assault weapon.
While there are people who seem to fetishize having a military styled weapon, there are practical merits to their use and ownership. I wish the "gun culture" here in the United States would do away with those glorification elements.
Hope that answers some questions and provides some insight.