One of the three guns Adam Lanza used to kill 20 children and six adults at an elementary school in Newtown, Connecticut, was a military-style semiautomatic rifle known as an AR-15. That surprised and shocked a lot of people unfamiliar with America's gun culture. They questioned why such weapons are available and why anyone would need them.

"Personally I don't know how any ordinary citizen can justify owning an automatic or semiautomatic gun," writes CNN commenter Mark Smerkanich. "Can't we leave those guns to the trained military?"

Self-described gun owner Julie Jones-Hawkins comments, "I ... fully support a ban on rapid-fire weapons. Any weapon that can take out an entire kindergarten class is a problem."

Here are five reasons many gun owners say they want military style rifles:

'Some people play golf, others bowl. I shoot'

"Every month or so I take my guns out to the range and shoot. It's thrilling, exciting and a great way to vent," says Christopher L. Kirkman, a Florida-based military-style gun owner.

Kirman was one of more than 100 gun enthusiasts who shared opinions on CNN iReport about owning firearms that would have been banned under the now-expired 1994 federal weapons ban.

"Sure, I could try to say that the reason I own these guns is self-defense, but the truth of the matter is that, although they will technically serve this purpose, they are not why I own them," he says.

Michigan gun owner Ethan Daniels describes his enthusiasm for his rifle more succinctly, saying, "I like to shoot, and that is one heck of a fun carbine to plink with."

Background can factor into a gun owner's choice of weapon. "The AR-15 is what I am used to from my extensive training as an airborne infantryman," writes Nathan Lee. "Because of my training, it's what I feel the most comfortable with."

Another reason for these guns is hunting. The AR-15 is a "good hunting platform. I've hunted coyote with it," says CNN iReporter MVR155, who owns two of the weapons. He asked to remain anonymous.

Owners of military-style rifles also use them to hunt deer and other game. But some states have banned the AR-15 and its .223 caliber for deer hunting.

'It's cool'

It may not be the best or most important reason, but military-style weapons often appeal to the enthusiast side of the American gun owner. Just like many car lovers who dream of owning a Lamborghini, many gun owners get excited about the idea of owning an AR-15.

"There are people who buy certain types of firearms because they have a certain image -- the AR-15 is one of them," says Austin Nikel, a former AR-15 owner in Boulder, Colorado.

"One thing about this country is how Hollywood has glorified the image behind those certain types of weapons. A lot of guys grow up with GI Joe, and that image is extremely attractive. It grabs you and affects you.

"A lot of people buy the AR-15 because, well, it's cool."

Apparently it wasn't cool enough for Nikel to hold on to. He ended up selling his AR-15 to his father.

'A part of history'

"Since coming of age -- and in the decades since -- I have collected many different firearms, some of them historical pieces, some for sport, some of them even the so-called 'assault weapons' that are now a controversy," says iReporter Hrothgar01.