Why is the AR-15 such a popular weapon for mass killers?

This video seems like a major clue.

I was looking on YouTube, and there are a lot of instruction videos on how to fire this and other semi-automatic weapons as a full-on automatic — what they call “bump firing.” I don’t see much difference between this an a machine gun –which probably has a lot to do with their popularity, and possibly made this model much more lethal in these recent mass killings:

There’s something about this Bushmaster AR-15: Both Adam Lanza and William Spangler, the two gunmen in the Newtown and firefighter shootings, respectively, got their hands on the same make of semi-automatic, the .223 caliber rifle, pictured right. This popular sporting gun seems to be the weapon of choice for many a mass murderer. It’s also the same gun used by James Holmes, of the Aurora theater shootings last summer, as well as Jacob Tyler Roberts, the mall shooter from a few weeks back. What is it about this Bushmaster that makes it so available and desirable for these gunmen?

For one, there are a lot of Bushmaster AR-15s out there. It’s one of the most popular sporting guns, noted Time’s Madison Grey. Lanza didn’t purchase his at a store, but rather, his mother, a “gun enthusiast,” had owned the guns, which is reportedly how Lanza got his hands on them. It is still not clear where Spangler got his Bushmaster. As a felon, it was illegal for Spangler to possess a firearm. So he must’ve gotten his hands on one already purchased. Between 2000 and 2010, the company sold over 2 million of the Bushmaster make. 1.5 million AR-15s have been sold in the last five years alone, according to Guns and Ammo. Also a testament to their wide popularity, the guns started flying off shelves after Newtown.

Some say that the rise in popularity has to do with more homeowners keeping them for protection, according to another Guns and Ammo article. Or, maybe it’s the idea of owning something so powerful, as Joseph Olson a professor and NRA board member explained to TPM’s Eric Lach. “It’s all cosmetics and it’s all marketing,” Olson said, adding, a bit later: “It’s the American consumer getting what they want.” Guess that Man Card marketing campaign has really worked.

Besides the wide availability, the gun’s lethality might give some insight into why these types of shooters seek to get their hands on one. Though the Bushmaster describes itself as a semi-automatic, dispensing only one bullet at a time, the civilian make of an M-16 can shoot lots of bullets very quickly. YouTube even has some tricks for turning a “semi-auto into a full-auto machine using a household rubberband!”