Just two days after Omar Mateen used a semi-automatic rifle to murder 49 innocent people and injure dozens more, we were able to purchase an AR-15 -- a rifle similar to Mateen’s that has been used in several other mass shootings on American soil -- in less time than it takes to buy a cart full of groceries. (Gillian Brockell/The Washington Post) 
 
 In the hours after Sunday’s mass shooting at an Orlando night club, Chief John Mina of the Orlando Police Department said the gunman’s weapons included a pistol and an “AR-15-type assault rifle.” 
 
 On Monday night, officials clarified that the rifle Omar Mateen used in the shooting was not an AR-15, but a Sig Sauer MCX rifle. The AR-15 has been the gun of choice in several other recent mass shootings, including the killing of 14 people attending a holiday party last December in San Bernardino, California; the murder of 12 in a movie theatre in Aurora, Colorado in 2012; and, later that year, the slaughter of 26 children and staff members at an elementary school in Newtown, Connecticut. There’s also, by design, a gas system that takes a lot of the gas from the firing of each bullet, and it evaporates it, so that when each bullet is fired, that gas and that recoil isn’t coming back on the shoulder each time, but it’s actually in the rifle in a more constructive manner. It’s hard to know whether Mateen’s AR-15-style weapon would have been covered by the old ban, though some versions of the Sig Sauer MCX rifle he used are sold with more than one of the components that were limited by the law. It is a shoulder-fired weapon that allows the shooter to select between semiautomatic (requiring you pull the trigger for each shot), fully automatic (hold the trigger and the gun continuously fires) or three-shot-burst mode. 1 of 25 Full Screen Autoplay Close Skip Ad × What the investigation into the Orlando mass shooting looks like View Photos Officials are scouring the site and others in the area for information about the June 12 massacre. The guns falling under the “assault” umbrella are “a set of quotidian weapons that have never posed much of a problem to anybody”.
– The Orlando shooting has raised anew the issue of the powerful weapons used by gunmen in mass shootings. While police initially said Omar Mateen used an "AR-15-type assault rifle," they have since clarified that he used a Sig Sauer MCX rifle. A look at some of the coverage: The Washington Post looks at those two weapons and finds that they're similar in broad terms: "a highly portable, customizable, easy to operate and accurate rifle." But one big difference is in the mechanics of how the bullet is propelled and the next round readied. It's "direct impingement" vs. "piston gun," as the Post explains here. The Sig Sauer can use magazines common to other semiautomatics, "but otherwise has no major parts that interface with AR-15s in any way, shape or form," says the Bearing Arms blog. (The post bashes media ignorance on the subject.) The Economist digs into the controversy over use of the term "assault rifle," which gun-rights advocates say is inaccurate because a gun such as the AR-15 "shoots only one round per trigger-pull." Orlando station WFTV offers a primer on topics such as the difference between semi-automatic and automatic weapons. (The AR-15 and the Sig Sauer are in the first camp; the military's M16 is in the latter.) PBS NewsHour did a segment on the AR-15 here. A Philadelphia Daily News columnist explains how she bought an AR-15 in seven minutes. Two Huffington Post writers got it done in 38 minutes. A New York Daily News writer fires an AR-15 for himself. He's "mostly terrified" as a result. Though he's taking flak for saying he got a temporary case of PTSD. FiveThirtyEight looks into the complicated topic of how such weapons are covered under gun laws.