If you were able to stomach any of the gruesome video or audio from the Las Vegas shooting last weekend, you may have noticed the rapid fire sound of what seemed like an automatic assault rifle.

But since 1986, it has been illegal to own basically any automatic weapons in the United States, with very few exceptions.

“So how did the Las Vegas shooter nearly replicate the destruction of a gun that has been illegal for more than 30 years?” a new video from Vox asks.

It turns out the shooter – 64-year-old Stephen Paddock – modified his legal AR-15A2 Sporter II Carbine with something called a “bump stock.”

A bump stock uses the kinetic energy from a gun’s recoil to push the weapon forward against the users trigger finger to simulate automatic fire. But since the attachment doesn’t modify the weapon’s firing mechanism, the $99 stock is legal to buy – online in many states.

Bump Stocks Come Under Fire on Capitol Hill – and the NRA Might Sacrifice Them

Shortly after it had become clear that the Las Vegas shooter had used one of these stocks – which surely helped to make his sinister deed much more deadly – the truth came out.

Many lawmakers didn’t even know what a bump stock was.

But you better believe they know now – and even Republican lawmakers have been open to considering whether bump stocks should be more tightly regulated, or even outright banned.

Usually, whenever there is a mass shooting, the NRA follows the same protocol: Say nothing for as long as possible, and use their deep coffers to staunchly oppose any change to gun laws or regulations – even the idea of the CDC studying gun violence.

This time might be different. The last two major mass shootings each broke the record for the deadliest shooting in American history, only a year apart from one another. As a result, people are fed up. The number of Americans open to some sort of change in gun legislation is only growing – on both sides of the aisle. In 2015, the PEW Research Center found that as many as 88% of Democrats and 79% of Republicans favored expanding background checks, for example.

Also, the NRA has become a huge political target. Opposition groups to the NRA – like Everytown for Gun Safety and Moms Demand Action – are growing, as is opposition on Capitol Hill.

And as online retailers began to pull bump stocks from their inventory, the NRA broke protocol and released a statement saying that bump sticks “should be subject to additional regulations.”

Of course, that’s to say nothing of an outright ban on the stocks, or any other type of firearms regulation. And the NRA may just be willing to throw gun safety advocates a small win so they can continue justifying their opposition to any kind of actual gun reform – even as yet another 58 people lie dead and 489 others wounded as the result of, yet another, mass shooting.