But if a reader had started on the page for either of Breivik’s guns, the Ruger or the Glock, they would not know this. That reader would find a great deal of technical information about the weapons in question – their weights, lengths, cartridges, rates of fire, magazine capacities, muzzle velocities – and detailed descriptions of their designs, all illustrated with abundant photographs and diagrams.
What do the perpetrators of the massacres at Sandy Hook, at Aurora, at Orlando, and at Sutherland Springs have in common? They were all men under 30 and they all used versions of the same kind of firearm, the AR-15, the semi-automatic version of the military's M-16 and the bestselling gun in America. It might be difficult to make this connection because as I write this, the section on the use of AR-15s in mass killings has been deleted from Wikipedia...
But on Wikipedia, as in the real world, the users with the deepest technical knowledge of firearms are also the most fervent gun owners and the most hostile to gun control. For critics, that’s led to a persistent pro-gun bias on the web’s leading source of neutral information at a time when the gun control debate is more heated than ever.
The bias in the articles was not explicit, but structural. The project did not insert false information into the articles, but instead purged information that showed the weapons in a bad light - dismissing it as "off topic".
A group of pro-gun Wikipedia editors tried to hide the true number of mass shootings associated with the AR-15 rifle in the aftermath of the Marjory Stoneman Douglas High School shooting in Parkland, Florida.
The Wikimedia Foundation has defended itself and Wikipedia from allegations of being host to these kinds of influence campaigns, arguing that the encyclopaedia is constantly being updated and improved.