Whether I ask for them or not, I am sent e-mails from the Coalition to Stop Gun Violence, and sometimes they contain interesting stuff. The latest one informed me that California's legislature has passed a law requiring that all automatic pistols sold in that state after 2010 have their breech faces and firing pins microengraved. This process would stamp the serial number of a gun on the case of any round it fired, enabling the police to trace the firearm from brass left at the scene of a shooting.