Fact checking the gun debate: a round-up Chris Dogolo, owner of Chris' Indoor Shooting Range, inspects a Colt Single Action Army revolver in Guilford, Conn. Since the Newtown shooting four months ago, the Fact Checker has devoted 14 columns to examining various statistics about guns and gun violence, as well as claims made in pro-gun and anti-gun advertisements. Yet some of these disputed facts keep turning up in the political discourse, and in news reports, even if many of the claims made by both sides simply do not hold up to scrutiny. Most recently, President Obama last week repeated the claim that 40 percent of gun sales lack a background check, even though the Fact Checker, PolitiFact and the Associated Press had pointed out the figure was unreliable. The president did not, however, repeat the statistic in his most recent speech on gun violence this week. Here, as a reader service, is a summary of our ratings on gun statistics, with links to the original columns in the headlines. We will continue to examine gun claims made on both sides, and welcome suggestions from readers. Concealed-weapon laws always result in less crime Here, we looked at a claim that "every time guns have been allowed, concealed-carry has been allowed, the crime rate has gone down." The actual evidence is much murkier - and in dispute. Certainly, it appears such laws have not increased the crime rate, as opponents had feared, but it is equally a stretch to say such laws are a slam-dunk reason for why crimes have decreased. We wavered between Two and Three Pinocchios, and ultimately settled on Three. Half of the mass killings in the history of the United States have occurred since the assault weapons ban expired in 2005 Former president Bill Clinton made this striking claim, but he was way off base. There are definitional issues, such as how one defines a mass shooting, but we found that just over 20 percent of all mass public shootings had taken place since the ban expired, which is much less than Clinton's 50 percent. He earned Three Pinocchios. NRA ad claiming the school attended by Obama's children has "armed guards" This National Rifle Association ad highlighted what the pro-gun organization saw as "elitist" hypocrisy by President Obama because his children are "protected by armed guards at their school." But this claim, which originated in the blogosphere, was false. Sidwell Friends school security officers do not carry guns. The NRA earned Four Pinocchios. Anti-NRA ad attacking lawmaker for accepting "NRA blood money" The target of this Coalition to Stop Gun Violence ad was Rep. John Barrow of Georgia - the last white Democratic member of Congress from the Deep South. The CSGV video intercut scenes from a campaign ad that Barrow ran in 2012, talking about his family's guns, with television footage of the massacre of school children at Sandy Hook Elementary School. But the group removed all of the language that Barrow used to explain why his family had such weapons - to deter crime and for protection. It also removed a reference to the Second Amendment, which President Obama has said he supports. The group earned Three Pinocchios. As many as 40 percent of all gun purchases are conducted without a background check We examined this claim in a series of three columns. The main issue is that this claim is based on a relatively small survey nearly two decades old, with some of the answers predating the enactment of the Brady law that mandated background checks. Moreover, the analysis concerned all gun transactions, not just sales, so when adjusted for just purchases, the percentage without checks dropped in half. Earlier this week, we downgraded the claim to Three Pinocchios. The Brady Law kept 1.5 million people from getting their hands on a gun This number has come under attack from gun-industry supporters as a bogus figure. There are certainly gaps in the information - and a lack of prosecutorial follow-up, which has further muddied the picture. Moreover, there are significant percentages of appeals and overturned referrals for prosecution. But the claims of an overwhelming number of "false positives" did not add up either. In lieu of more evidence showing this was an inaccurate fact, we concluded this figure rated a rare Geppetto Checkmark. Obama's background check plan amounts to a "thinly veiled national gun registration scheme" This is a common claim by pro-gun advocates, and we examined in particular an assertion by the campaign manager for Senate Republican Leader Mitch McConnell (Ky). But current law specifically prohibits using the National Instant Criminal Background Check System (NICS) to create a federal firearms registry - a law which McConnell help passed. This claim earned Four Pinocchios. More than 20,000 gun laws are already on the books It turns out a version of this claim has been made repeatedly by pro-gun advocates for five decades. But, by any reasonable measure, this is suspicious figure. Its origin is murky, and it is inconceivable that the same number of gun laws would exist now as some five decades ago. Moreover, even experts who favor the NRA's agenda have their doubts about the figure or its relevance. We concluded the 20,000 figure appears to be an ancient guesstimate that has hardened over the decades into a constantly repeated, never-questioned talking point. It earned Three Pinocchios. The NRA has 4.5 million active members Readers had questioned whether the NRA could have gained 500,000 members in just six months. Using NRA magazine subscriptions as a guide, we were inclined to conclude that the NRA is overestimating the size of its membership, and it appears possible that the membership rolls are below 4 million. We said we would tentatively award this claim One Pinocchio, but would revisit this ruling if more data emerge or if the magazine subscriber base demonstrates a steep jump in the next report. Bloomberg PAC anti-gun ads targeting Democrat in Illinois We examined an ad underwritten by an anti-gun organization funded by New York Mayor Michael Bloomberg, which attacked former Rep. Debbie Halvorson of Illinois for her gun positions. We found the ad mischaracterized her current positions, and it earned Two Pinocchios, but she lost her effort to win the Democratic nod in a House special election. Was Biden's shotgun advice "illegal"? The NRA poked fun at the vice president for urging women to fire a shotgun in the air to ward off a potential intruder, saying it illegal. The NRA made a compelling case that Biden's advice, if taken, would violate a number of Delaware laws. But the state prosecutor - appointed by Biden's son - disagreed and said no action would be taken. Given the maze of conflicting interpretations, we issued no ruling. There are 9,000 people in 2010 that failed a background check who are felons on the run, and none of them were prosecuted This claim by Sen. Lindsey Graham (R-S.C.) gave us another opportunity to look at the data concerning prosecutorial follow-up on failed background check applications. While there is no nationwide survey, the available evidence showed that at least some fugitives are identified through the background system and subsequently pursued at the state level for prosecution. His sweeping claim of "none" earned Three Pinocchios.