This question has been bandied about by people who don't know guns, as some sort of rhetorical trump. The answer is somewhat complicated for people not versed in the subject, but I'm going to have a whack at it.
The AR15 is a development of an earlier rifle in a larger caliber—the .308 caliber AR10. The "AR" is from Armalite, the designing company, which at the time (early 1950s) was a division of Fairchild Aircraft. Some of the most sophisticated alloys and machining techniques were used in its development.
Keep that timeline in mind—1950s. AR15s have been in military use since 1959, and on the civilian market since 1963—longer than most of you have been alive. If you're just now becoming aware of them, you're 50 years, half a century, behind the curve. There have been improvements in this time, but it's been around for two generations. This might even be your grandfather's gun. The 30 round magazine, by the way, has been STANDARD CAPACITY for 40 years. You don't get to redefine it as "high capacity" just because you've recently become aware of it.
The AR15 receiver is made of light, very strong aluminum alloys, to quite tight tolerances. The barrel and operating parts are various steel alloys, chosen for specific characteristics. The gun weighs 5-9 lbs depending on configuration. This is quite light, at the bottom end for rifles, which makes it easier to handle for smaller people. It's a fact that without the AR15, and its military analog the M16 (which fires in full auto or burst, which civilian AR15s are not capable of), there would be a lot less women in the armed forces or shooting sports. Not only are earlier self-loading rifles heavier, they usually have heavier springs and operating masses, beyond the capability of many women and smaller men, and youths, to operate.
Also, the AR15 operates by what is called "direct gas impingement." Instead of using barrel gas pressure to shove a piston to work the action, the gas directly hits the bolt carrier—the cycling part of the action. There are pluses and minuses to this, but the big plus is a much lighter operating mass. That means a lot less recoil, which makes shooting easier, and more accurate, for everyone, and makes it usable by some small people for whom a bigger rifle would cause bruising and injury.
It generally comes in 5.56mm, or .223 Remington, developed from what was considered a "varmint" round in the 1950s. Again, there are pluses and minuses. One plus is that a lighter cartridge means even LESS recoil. So again, there's an advantage for smaller people. It's still an advantage to larger people, because recoil itself doesn't offer ANY advantage. It's a side effect of shooting. The less side effect, the better. Also, it's more powerful than a handgun. The recent case of a lady firing 5 shots from her revolver http://www.cbsnews.com/8301-504083_162-57562397-504083/georgia-mother-hides-children-shoots-intruder-5-times-during-home-invasion-police-say/ without reliably stopping the attacker is an indication that handguns have limitations.
I mentioned "5-9 lbs depending on configuration." The AR15 is a brilliant design that can be changed in caliber, barrel length and even stock type in a few moments, literally a matter of seconds for most changes in barrel or caliber, by swapping out an entire assembly held in place with two pins. You can shoot .22 for practice, .223 for varmints, or .458 SOCOM in a carbine length for home invaders. You can attach a heavier barreled assembly for long range target shooting or sniping.
And the adjustable stock, that 'evil feature' that makes it an 'assault weapon' to some people, means it can be adjusted to fit shooters of different statures or wearing various clothing –parkas vs T-shirts.
Detachable magazines do enable faster reloading, which is a good thing. Fumbling with a gun while someone is trying to kill you is a bad thing. Also, a detachable magazine makes it easier to UNLOAD a weapon, which also increases safety.
So, it's a light, versatile, reliable, accurate, easy and safe to use weapon that is excellent for home defense, pest control, recreational shooting and making a political point against invaders and tyrants. Every home should have a few.
As far as the AK47, it has some advantages over the AR15, some disadvantages, and generally costs ½ to 2/3 as much, so it's better for people on a budget.
Now, let's address some of the snide comments people are going to want to post.
Its political opponents like to bleat, "Guns are only good for killing," as if they've discovered some profound revelation, are standing on some moral peak, or have played some kind of trump.
Well, no, that is not true. However, as far as killing, or at least stopping people, it is pretty good, and quite accurate. They also seem to think that killing is a bad thing. It's not. Murder is a bad thing. Killing should generally be avoided, but thousands of years of Common Law, and most state laws, do not prohibit the killing of an attacker, if your own life is threatened. And unless you're Chuck Norris, an AR15 is a much better tool for this than your fists or a kitchen knife.
There's also the possibility of local or national insurrection or despotism. While the US has avoided this so far, it is not an impossibility. It has happened in dozens of prosperous, liberal nations over the last century. If you deny this fact, or the possibility, please stop reading now and go back to your reality shows.
Don't take my word for it, though. Let's see what the Supreme Court has to say:
There are many reasons why the militia was thought to
be “necessary to the security of a free state.” See 3 Story
§1890. First, of course, it is useful in repelling invasions
and suppressing insurrections. Second, it renders large
standing armies unnecessary—an argument that Alexander
Hamilton made in favor of federal control over the
militia. The Federalist No. 29, pp. 226, 227 (B. Wright ed.
1961) (A. Hamilton). Third, when the able-bodied men of
a nation are trained in arms and organized, they are better
able to resist tyranny.
Cite as: 554 U. S. ____ (2008)
The most significant of these commentators was Joseph
Story. Contrary to the Court’s assertions, however, Story
actually supports the view that the Amendment was
designed to protect the right of each of the States to maintain
a well-regulated militia. When Story used the term
“palladium” in discussions of the Second Amendment, he
merely echoed the concerns that animated the Framers of
the Amendment and led to its adoption. An excerpt from
his 1833 Commentaries on the Constitution of the United
States—the same passage cited by the Court in Miller34—
merits reproducing at some length:
“The importance of [the Second Amendment] will
scarcely be doubted by any persons who have duly reflected
upon the subject. The militia is the natural defence
of a free country against sudden foreign invasions,
domestic insurrections, and domestic usurpations of
power by rulers.
...."The right of the citizens
to keep and bear arms has justly been considered
as the palladium of the liberties of a republic, since it
offers a strong moral check against the usurpation
and arbitrary power of rulers, and will generally, even
if these are successful in the first instance, enable the
people to resist and triumph over them."
3. Relationship between Prefatory Clause and
We reach the question, then: Does the preface fit with
an operative clause that creates an individual right to
keep and bear arms? It fits perfectly, once one knows the
history that the founding generation knew and that we
have described above. That history showed that the way
tyrants had eliminated a militia consisting of all the able bodied
men was not by banning the militia but simply by
taking away the people’s arms, enabling a select militia or
standing army to suppress political opponents. This is
what had occurred in England that prompted codification
of the right to have arms in the English Bill of Rights.
also cite as support Tucker and Rawle, both of
whom clearly viewed the right as unconnected to militia
service. See 3 Story §1890, n. 2; §1891, n. 3. In addition,
in a shorter 1840 work Story wrote: “One of the ordinary
modes, by which tyrants accomplish their purposes without
resistance, is, by disarming the people, and making it
an offence to keep arms, and by substituting a regular
army in the stead of a resort to the militia.” A Familiar
Exposition of the Constitution of the United States §450
(reprinted in 1986).
All from District of Columbia vs Heller, 2008.
There. Several references to being able to fight a tyrannical government, all from four years ago, from the highest court in the land. DC lost, by the way.
So, yes, the AR15 is made to kill people, and there are some people who need killing, so says common law, codified law, and the Supreme @#$ing Court. Therefore, if you say, "The only purpose of a gun is to kill people," you're not entirely correct, but you are in fact making a statement that supports gun ownership. Thanks. We're glad you've figured it out. One of the main purposes of guns is to kill people who need killing.
"When all you have is a hammer, all your problems look like nails."
No. However, when the problem IS a nail, beating it with a screwdriver accomplishes nothing, and beating it with your fists only causes injury to yourself. One well-placed hammer blow makes the problem go away. Thanks for playing.
Just to reinforce this, here's the money quote from Heller:
"Some have made the argument, bordering on the frivolous, that only those arms in existence in the 18th century are protected by the Second Amendment. We do not interpret constitutional rights that way. Just as the First Amendment protects modern forms of communications, e.g., Reno v. American Civil Liberties Union, 521 U. S. 844, 849 (1997), and the Fourth Amendment applies to modern forms of search, e.g., Kyllo v. United States, 533 U. S. 27, 35–36 (2001), the Second Amendment extends, prima facie, to all instruments that constitute bearable arms, even those that were not in existence at the time of the founding."."
In America we have a constitutional right to own modern firearms for the purpose of killing people who need killing to defend ourselves, our communities and our nation. If you don't like it, there is no law stopping you from leaving. In fact, as an immigrant myself, I'd encourage you to find a nation better suited to your philosophy, as I did, and move there, as I have done. In exchange, I have friends and relatives overseas who'd be happy to swap with you.
And my daughter thinks you're a sissy: