What is the AR-15, and what makes it special?
The AR-15 is a semiautomatic civilian version of an M-16 military machine gun. It is not a true assault weapon, since it can't fire continuously. It's extremely accurate at 200 yards and easy to modify, and thus has many uses, ranging from coyote hunting to hobby shooting at ranges. Its short barrel and modified stock makes it easy to maneuver in tight places, making it a popular home defense weapon as well. A variety of gun companies make their own versions of the basic frame, and quality and price fluctuate from company to company.
How many assault-style weapons are in circulation in the US?
Gun manufacturers don't break sales down by product, so it's hard to know exactly. But a solid back-of-the-envelope estimate developed by Slate's Justin Peters suggests that there are about 3.75 million AR-15-style weapons in circulation today, with companies like Sturm-Ruger & Co. Inc., headquartered in Southport, Conn., producing perhaps 200,000 of them a year for sale in the US.
As popular as the iPod, though?
Maybe not quite. With 310 million firearms in circulation, AR-15s make up barely more than 1 percent of the total. But given that stores are struggling to keep the weapons in stock, acknowledging the 2.48 million background checks in January (an increase of more than 50 percent since 2007 monthly averages), and noting that Apple sold 5.3 million iPods in the last quarter of 2012, it's not hard to extrapolate the AR-15's immense popularity as a consumer good. And, like iPods, the guns are not cheap: An AR-15 usually costs between $600 and $1,000 but are often selling upwards of $2,000 lately.