Firearm microstamping, ballistic imprinting, and ballistic engraving are all names given to a controversial technology that has been developed with the goal of aiding in ballistics identification. It involves the use of laser technology to engrave a microscopic marking onto the tip of the firing pin and onto the breech face of a firearm. When the firearm is fired, these etchings are transferred to the primer by the firing pin and to the cartridge case head by the breech face, using the pressure created when a round is fired. After the spent cartridges are ejected, these microscopic markings which have been imprinted on the cartridges can then be recovered by police and examined by forensic ballistics experts to obtain information to be used to trace the firearm through its life to the registered owner. This technology was to be required in California starting in 2010, however, it is on hold and law enforcement is specifically exempt. On May 17, 2013, California Attorney General Kamala Harris announced that micro-stamping had cleared all technological and patenting hurdles and would be required on newly sold semiautomatics, effective immediately. However, handguns already approved for sale but lacking this technology may still be sold as long as they remain on the Roster of Safe Handguns. 
In general, groups that support gun control legislation favor requiring ballistic imprinting on all new firearms, while groups supportive of gun rights generally oppose any legal requirement for ballistic imprinting technology. Since the technology is unproven with large scale implementation, there are no reliable statistics to substantiate how useful the process might really be to law enforcement or that it would in any way hurt these same efforts. An unintended consequence of the firearm microstamping law in California is that gun manufacturers, such as Sturm, Ruger & Co., as well as Smith & Wesson, have chosen simply to stop selling guns in California, rather than to comply with the requirements of the law.
Claims made by proponents of the technology include:
- Microstamping enables law enforcement to match fired cartridge cases from a crime scene to at least the last registered owner of the firearm.
- Microstamping would allow law enforcement to track illegal trade in guns.
- Low cost of implementation; the technology owner claims as low as US$0.50 per firearm or as high as US $8.50, depending on the volume of the manufacturer.
- High reliability; the "nearly as hard as a diamond" firing pin provides long service life.
Claims made by the opponents of the technology include:
- Stamped casing can only be traced to the last registered owner, not to the person who used the gun when the casings were stamped. In the case of a stolen gun, as is the case for most firearms used in crime, the stamped case would not lead to the criminal.
- Unscrupulous individuals could collect discarded brass from a firing range and salt crime scenes with microstamped cases, thereby providing false evidence against innocent people and increasing the workload for investigators.
- High costs for testing the efficacy of the technique must be passed on to customers, increasing the cost of firearms for those who obtain them legally.
- Microstamping is easily defeated. Diamond coated files are inexpensive and will remove microstamping. Firing pins are normally replaceable and can be changed with simple tools or without tools. Firing a large number of rounds will wear down the microstamp. Marked components such as slides, barrels, firing pins and ejectors are all easily and commonly replaced items.
- Microstamping is an immature, sole source technology, and has not been subjected to sufficient independent testing. Transfer of microstamped marks to the cases is less reliable than proponents claim.
- Microstamping would be irrelevant/non-applicable for implementation of revolvers as these types of weapons do not eject shell cases necessarily.
- Ejected casings can be easily collected and removed from a crime scene.
Specific to California, opponents say:
- Firearms sold to law-enforcement are exempt. Problems could arise if a police officer's firearm is used in a crime or stolen, and the fact that a firearm is "unsafe" if not provided with stamping technology exposes the police to liability.
- Guns manufactured before an effective date are exempt and the bill does not extend to guns outside of California. There's no possibility that this bill would ever cover enough guns to provide the investigative advantage claimed for it by the proponents.
Associated legal issues
The issue of liability for the gun owner if the firing pin is replaced or if the chamber marking is removed may constitute violating federal and/or state statutes that impose strict penalties for defacing the serial numbers of firearms. However, in an amendment proposed to the bill passed in California AB 1471, this issue is addressed, at least for the state level:
- "The microscopic array of characters required by this section shall not be considered the name of the maker, model, manufacturer's number, or other mark of identification, including any distinguishing number or mark assigned by the Department of Justice[of California], within the meaning of Sections 12090 and 12094."
The microstamp is therefore not considered the serial number in California law, for the intents and purposes of the California penal code. It is still unclear if such penalties may be prosecuted at the federal level, as there is no concrete definition of a "manufacturer's serial number."
It would also be possible for someone planning a criminal act to obtain fired casings with markings from a shooting range, for planting at the scene of a planned crime, erroneously linking unrelated gun owners to the crime scene to introduce doubt in any subsequent jury trial. Similarly, as microstamping is meant to leave distinguishing marks both on the primer and the case head, range brass, acquired at a range and reloaded, would still be marked with confusing markings on the head of the cartridge case.
Legal jurisdictions in the United States
- States using microstamping
- States considering microstamping
Similar legislation is under consideration in New York, Connecticut, Rhode Island, Massachusetts, Maryland, Wisconsin, and Illinois.
- Federal legislation
Federal bill H.R.5266, the National Crime Gun Identification Act of 2008, was written by House Rep. Xavier Becerra (D-CA). Senator Edward Kennedy (MA) introduced an identical companion bill in the Senate.
- "Smith & Wesson says it won't follow California 'microstamping' law". Retrieved 24 January 2014. "Gun manufacturer Smith & Wesson refused Thursday to comply with California's controversial "microstamping" law, causing more of its products to fall off the state's permissible firearms list and be ineligible for sale."
- Page, Douglas. "Microstamping Calls the Shot: A Revolutionary Gun Identification Technology Finds Favor and Foes". National Crime Justice Reference Service. Retrieved 21 September 2010.
- "Cracking the Case: The Crime Solving Promise of Ballistics Identification." Educational Fund to Stop Gun Violence Report on Microstamping, 2004. Report
- Cal. P.C. § 12125(b)(4)
- "Smith & Wesson says it won't follow California 'microstamping' law". Retrieved 24 January 2014.
- SAAMI. "AB 352 Defines As "Unsafe" Any Semi-Automatic Pistol Not Microstamped". Archived from the original on 2007-07-06. Retrieved 2007-11-26.
- See accurizing
- Mike Feuer. "City of Oakland Bill Analysis". Retrieved 2007-11-27.
- California Assembly (AB 1471)
- Sections 12090 and 12094 of the California Penal Code CA Penal Code
- US Title 18 Chapter 44 Section 921 and 922(k) US Penal Code
- Albany Times Union
- Gun Owners of California report on AB 352
- UC Davis Forensic Science report on firearms microstamping, corrected revision here
- See a presentation on Capitol Hill about the technology by the developer and some others: Part 1, Part 2, Part 3, Part 4, Part 5, Part 6
- Coalition to Stop Gun Violence (CSGV) Microstamping Page
- NSSF Factsheet "Microstamping Technology: Proven Flawed and Imprecise"