In 1969, President Lyndon B. Johnson's National Commission on the Causes and Prevention of Violence recommended "a system of giving each gun a number and the development of some device to imprint this number on each bullet fired from the gun." In modern form, the concept, now termed "micro-stamping," theorizes that a firearm's firing pin or other internal parts could bear microscopic codes unique to the firearm and imprint the codes on fired cartridge cases, that the codes could be entered into a computerized database before the firearm leaves the factory, and that police investigators could pick up a cartridge case left at a crime scene, identify the markings on the case, run them against the database, and identify the criminal involved. "Micro-stamping" legislation supporters claim it will help police solve crimes, but their real purpose is to price handguns beyond the reach of many Americans, by requiring firearms to be made with the gadgetry necessary to create the markings, or to ban handguns by requiring that they "micro-stamp" more consistently than is technologically possible.

In 2007, California adopted a "micro-stamping" law that, as of 2010, will prohibit, as an "unsafe handgun," newly-designed semi-automatic pistols not equipped with two or more internal parts that imprint, onto the cartridge case of a fired round of ammunition, a microscopic array of characters that identify the pistol's make, model and serial number.¹

In 2008, Sen. Edward Kennedy (D-Mass.) introduced a bill, supported by Sen. Barack Obama (D-Ill.), to require "micro-stamping" technology in new handguns. Another bill (H.R.1874), by Rep. Robert Andrews (D-N.J.), proposes to prohibit any firearm that doesn't "micro-stamp" with every type of ammunition, every time.

Problems with "Micro-Stamping"

• "Micro-stamping" has repeatedly failed in tests. In 2006, a study at the University of California (Davis) concluded, "At the current time it is not recommended that a mandate for implementation of this technology in all semiautomatic handguns in the state of California be made."² Results of the study were consistent with earlier peer-reviewed tests published by the Association of Firearms and Toolmarks Examiners.³ Firearms examiner George Krivosta, of the Suffolk County, N.Y., crime lab, found that the "vast majority" of "micro-stamped" characters in the alphanumeric serial number couldn't be read on "any of the expended cartridge cases generated and examined."
• "Micro-stampings" are easily removed. In the tests noted above, firing pins were removed in minutes, and serial numbers were obliterated in less than a minute, with household tools.
• Most gun crimes cannot be solved by "micro-stamping," or do not require "micro-stamping" to be solved. Most gun crimes do not involve shots being fired, thus there are no cartridge cases for police to recover. Also, a large percentage of gun crimes involve guns that don't eject fired cartridge cases. Notwithstanding TV shows that portray crime-solving as impossible without high-technology, most crimes can be solved by traditional means. For example, of murders in which the victim-offender relationship is known, 77% involve family members, friends and other acquaintances. Only 23% involve strangers.⁴
• Most criminals get guns through unregulated channels. According to the BATFE, 88% of crime guns are acquired through unregulated channels, and the median time between a crime gun's acquisition and its use in crime is 6.6 years.⁵ According to the Bureau of Justice Statistics, most criminals get guns via theft or the black market.⁶
• "Micro-stamping" would increase gun thefts, home invasions and burglaries, and expand the black market in guns. Criminals would be further encouraged to get guns illegally, if guns bought legally would be linked to them in a computerized database.
• Most guns do not automatically eject fired cartridge cases. Revolvers can fire five or more rounds without fired cases being ejected. Pump-action, bolt-action, lever-action and other types of guns eject fired cases only if the user manually operates the gun's unloading mechanism.
• Only a small percentage of guns would be "micro-stamped." There are 250+ million guns in the country.⁷ New guns sold annually account for only 2% of that total, and new semi-automatic pistols less than 0.5%.⁸
• Most violent crimes don't involve guns. According to the FBI, 3/4 of violent crimes, including 1/3 of murders and 3/5 of robberies, are committed without guns.⁹
• "Micro-stamping" would waste money better spent on traditional crime-fighting and crime-solving efforts. The cost of a computerized database to track "micro-stamped" handguns would be passed along to all consumers, including law enforcement agencies. It would require a redesign of the handgun manufacturing process, and could require payment of licensing fees to the sole-source "micro-stamping" patent holder.
• "Micro-stamping" would expose police departments to lawsuits if officers fired "unsafe handguns." Departments would have to spend money destroying all cases fired in training, to prevent cases from being reused at crime scenes. Criminals could obtain fired cases from practice ranges, and use them to "seed" crime scenes, to confuse investigators. 

1. California has repeatedly expanded its "unsafe handgun" ban. In 2001, it defined "unsafe handguns" as those that did not pass a drop test and a live-fire/malfunction test, and that did not have certain types of mechanical safeties. In 2006, the ban was extended to semi-automatic pistols that did not have a loaded chamber indicator or a magazine disconnect. In 2007, it was extended to semi-automatic pistols that do not have an indicator and a disconnect.

2. David Howitt, et al., "What Laser Machining Technology Adds to Firearm Forensics: How Viable are Micro-Marked Firing Pins as Evidence?," 2007.

3. George G. Krivosta, "NanoTagTM Markings From Another Perspective," 38 AFTE Journal 41, 2006.

4. FBI, http://www.fbi.gov/ucr/cius2006/offenses/expanded_information/data/shrtable_09.html.

5. BATFE, Crime Gun Trace Reports 2000, National Report, http://www.atf.gov/firearms/ycgii/2000/highlights.pdf.

6. Bureau of Justice Statistics, "Firearm Use by Offenders," http://www.ojp.usdoj.gov./bjs/pub/pdf/fuo.pdf.

7. National Research Council, Firearms and Violence: A Critical Review, National Academies Press, 2005.

8. BATF, "Firearms Commerce in the United States 2001/2002," http://www.atf.gov/pub/index.htm - Firearms.