"1993, G19 Upgrade Glock Model 19, 9mm Luger caliber, requires an upgrade for all pistols. These pistols have the potential for an UNINTENTIONAL DISCHARGE of a cartridge with the action open. The Glock model 19 pistol slide has a bottom protrusion, whose function is to push cartridges from the top of the magazine into the chamber. When the pistol is jammed in a double feed situation, the slide protrusion can come in contact with the primer of the jammed cartridge and cause UNINTENTIONAL DISCHARGE while the action is open." The quote above is from the serial number thread. The source for that quote is noted elsewhere as "AFTE Journal, July 1993; Volume 25, Number 3:206-208." I have searched and googled and have been unable to find a definitive answer as to what it is all about. I called Glock and spoke to someone in the Warranty department who said he knew nothing about it. Does anybody know for sure what this refers to? Thanks.