Opinion is divided this morning on Twitter among people who, unlike me, know more than the most basic basics about firearms. It’s not a matter of mere curiosity; as you (should) know, fully automatic weapons have been illegal in the U.S. for decades, which is why even mass shooters hellbent on murder unto death never use them. If Stephen Paddock used a machine gun, how on earth did he get it?

That’s a big “if” but listen to the shots in the clip below. The rate of fire is fantastically fast, way too much for a “one pull, one shot” semiautomatic. That’s an automatic, no?

Charles Cooke, an actual firearms expert, says it does sound like an automatic. And if it is, that means Paddock did a *lot* of planning for mass murder:

Jazz raised the possibility in his post that Paddock, as a 64-year-old man, may have bought an automatic before the 1986 ban on transfers and kept it around. Another possibility is that Paddock bought a standard semiautomatic and altered it to make it fully automatic, using a tutorial that he found online. That would also be difficult, though, according to Sean Davis, another gun expert:

Cooke agrees that it’s difficult. And, more importantly, the altered product is unreliable and apt to break quickly. I wonder if that explains the curious detail, flagged by Jazz, that Paddock allegedly had more than 10 rifles in his room. Why would a man with an automatic weapon need any other guns? One possible answer: If his automatic had been altered and he knew it was likely to break down during the attack. What if Paddock altered a bunch of other semiautomatics too, expecting that he’d run through them sequentially as one after another failed?

But maybe the weapon wasn’t automatic. There are things you can do to a semiautomatic to simulate automatic fire. Gun aficionados on Twitter are mentioning a “bump fire stock,” which uses the gun’s own recoil to fire quickly, as a possible explanation. Others, though, claim they’ve never seen bump fire continue for as long, and as consistently, as you hear in the Vegas video. Another alternative is a “Gatling crank,” which is just what the name implies — it attaches to the trigger of a standard semiautomatic like an AR-15 and, by turning the crank, generates much faster trigger pulls than a finger would be capable of, simulating a Gatling gun. Cooke thinks that’s possible as an explanation for Vegas, but compare the sounds of the shots in the Gatling crank clip I linked to the sounds in Vegas. The latter again seems a bit more consistent than the former.

Vegas police will have more to say. If this was a modified semiautomatic rather than a full automatic, Trump and the GOP will come under heavy pressure to ban whatever the modification was, whether a bump stock, a Gatling crank, or something else. Whatever the weapon ends up being, though, there’s no question Paddock planned extensively: In addition to the 10+ rifles, he reportedly requested a corner suite at Mandalay Bay, giving him more angles from which to fire, and had cameras set up so that he’d know when police arrived. The only thing he didn’t plan on was … smoke. Smoke from his weapon firing apparently set off the fire alarm in his room, giving Vegas cops his precise location very quickly. Imagine how many more might have died if it had taken, say, three extra minutes to track him down.

Update: Yet another possibility: The “auto glove.”

Update: Turns out the ATF declared the “auto glove” illegal as a de facto machine gun just two weeks ago.