In the wake of the Las Vegas mass shooting, U.S. House Speaker Paul Ryan says he's open to a vote in Congress on what is known as a "bump stock," a device that can be attached to a semi-automatic rifle that allows it to mimic a fully automatic one.

The Janesville Republican made his remarks on MSNBC's Hugh Hewitt talk show, which aired Saturday.

"I didn't even know what they were until this week, and I'm an avid sportsman," Ryan said of bump stocks. He added: "Fully automatic weapons have been banned for a long time. Apparently, this allows you to take a semiautomatic, turn it into a fully automatic, so clearly that's something we need to look into."

Twelve of the rifles police found in Las Vegas gunman Stephen Paddock’s Mandalay Bay hotel room were equipped with bump stocks. The increased rate of fire likely was a factor in Sunday's shooting, with 58 dead and 489 wounded.

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In the simplest terms, "semi-automatic" refers to any firearm designed to fire one bullet with one trigger squeeze, then automatically reload the chamber with a cartridge from a magazine and be ready to fire again. Automatic weapons, which are often described as machine guns, are different, in that squeezing the trigger once fires cartridges repeatedly until the shooter releases it.

Semi-automatic rifles are widely available, fully automatic weapons are not. Despite what Ryan said, it's possible to buy automatic weapons, but their sale and ownership are highly regulated and exceptionally expensive.