The AK47 is a Russian automatic rifle, caliber 7.62x39. Legal semi-auto only copies of the AK47 are common in the USA amongst law-abiding gun owners. Fully automatic versions are not legal unless it is a pre-1986 registered "machine gun" and those are so rare and prohibitively expensive that they are limited to collectors. The true maximum effective range of an AK is about 300 yards. AK's are typically not very accurate, anywhere from 3-5 inch groups at 100 yards is the norm, and some shoot even worse than this. This lack of accuracy combined with the bullet's arcing trajectory, limit the range to about 300 yards for combat purposes in the hands of a trained soldier. For hunting/civilian use, the effective range is really about 100 yards or so (to hunt deer, the rifle must be able to keep all it's shots within a 8 inch group at 100 yards, minimum). Many jurisidictions have banned/regulated AK47-type rifles based on their appearance and on political misinformation. In fact, it's 7.62x39 cartridge is a intermediate-powered round, ballistically equal to .30-30 Winchester, but usually loaded with inferior FMJ bullets as opposed to JSP in the case of hunting rounds for the .30-30. Conventional deer rifles in calibers like .308, .30-'06, .300 Winchester Magnum, etc, are significantly more powerful than the AK47 and it's 7.62x39 round. The AK is known for being a simple, inexpensive, reliable and effective weapon. Contrary to popular belief, criminals seldom use AK47's or other assault weapons because their size makes them impractical for criminal use. You can't hide one of these weapons under your coat when trying to rob a convenience store, after all. Criminals use whatever weapons are available and convenient for them, which almost always means cheap pistols/revolvers and the occasional illegally-modified short barreled shotgun (legal short barreled shotguns require registration with the ATF and paying a $200 tax, as well as law enforcement approval). Many other automatic rifles were derived from the AK, designs such as the Israeli Galil series, Finnish Valmet series of rifles, the Belgian FNC, Swiss SIG55x series of rifles, etc. The AK uses a simple gas piston in the tube above the barrel to drive the cam-roatating bolt action using gas pressure tapped off the barrel when the weapon is fired. This is how the weapon is able to rechamber between shots (why it's semi-automatic). Military AK variants are capable of automatic fire at about 600 rounds a minute, but because of recoil, automatic fire needs to be limited to short bursts of 2-3 rounds for it to be effective. Automatic AK's are not legally available in the USA because of the provisions of the National Firearms Act of 1934 (establishing law enforcement approval, the $200 tax, etc) followed by the 1968 Gun Control Act, which banned the import of automatic weapons for civilian use, then the Firearm Owners Protection Act of 1986 which banned all manufacture of new fully automatic weapons for civilian use. So to own an automatic AK legally, you have to find a pre-1986 registered weapon, find a Class III dealer to do the transfer for you, then you have to go through the ATF paperwork and get the local PD chief to approve you, then you pay a $200 tax stamp to the ATF, then you have to buy the actual weapon. Usual going price for a legal, fully-automatic AK that is available to be transferred is anywhere from $10,000-$15,000. For civilian use, the semi-automatic AK variants are very fun range plinking (informal target shooting) guns and can be used effectively to hunt deer and similar game, even though there are better rifles for this purpose. The AK would be a very good rifle for property defense in rural areas, not so good for home defense because of the extreme overpenetration hazard of 7.62x39 FMJ ammo (and the relative non-existence of JHP ammo that actually expands properly) and because of the muzzle flash, which could easily blind a person at night. For home defense, use a 12 gauge loaded with OO Buck, standard power loads because you want a easy-handling gun for that purpose. While many people feel the AK has no civilian use because of it's history as a military weapon, it's simply a fun, inexpensive, interesting rifle for many shooters.
"My friends and I enjoy shooting our AK47's at the rifle range on the weekends"