With the solid crack of a crowbar, the hooded burglar sent the showcase glass showering onto the gun shop’s floor and quickly swept several pistols into his shoulder bag. Among the cache that New Year’s morning at a northern Wisconsin gun shop was a lightweight 9mm handgun with a black polymer grip, a black steel slide and a 4½ inch barrel. On one side was the stamp of the handgun’s unique serial number: YZC020. On the other, the logo of one of the most profitable and ubiquitous firearms companies in the world: Glock. The Austrian handgun, a model 17, had...