Pennsylvania Attorney General Josh Shapiro announced on Monday that the biggest gun show promoter in Pennsylvania has banned the sale of so-called “80 percent receiver” kits, a common basis for untraceable homemade ghost guns. Shapiro said at a March 15 press conference that Eagle Arms Productions has agreed to stop selling the kits at its shows, marking the first time a gun show promoter in the United States has prohibited the sale of the 80 percent receivers. The kits, also known as “80 percent lowers,” are controversial because they are typically sold without background checks, and can be quickly and easily assembled into a fully-functioning firearm that lacks a serial number and so essentially cannot be traced. Makers of the kits, such as JSD Supply, tout their services are a response to restrictions around gun purchases. “Since 2013, we’ve helped thousands of people build their own gun from the privacy …