By Attorney Patrick Noaker, October 26, 2015
Everyone has a favorite CSI television show where the forensic investigator evaluates the crime scene and finds direct evidence that leads to the identity of the perpetrator. It is common for these shows to depict a number of weapon or ballistics evidence as evidence providing the absolute identity of the person who committed the crime. The reality is that many things must align in order for firearm ballistics evidence to be helpful in a criminal investigation. And even then, this evidence does not provide absolute identity.
Firearm ballistics identification is concerned with determining whether a bullet, cartridge case, or other ammunition component, was fired by a particular firearm. This issue normally arises when a bullet, cartridge or shell is found at a crime scene and a firearm is found somewhere else. The assumption behind this forensic science is that each firearm has unique characteristics that produce spent cartridges/shells and bullets with identifiable characteristics that can only be matched to that one firearm.
There are times that it is important to match cartridges to firearms. This is most common when analyzing a shooting scene that contains cartridges or shells. Initially, one can generally conclude that a shot was fired if there is a spent cartridge or shell.
At times, the location of the spent cartridge/shell can be very important to a crime scene investigation. Some shotguns and semiautomatic pistols and rifles automatically eject spent cartridges from the firearm. Depending on the model of the shotgun, pistol or rifle, the cartridge/shell will be consistently ejected in a particular direction and general distance. Although imprecise, crime scene investigators can use the location of cartridges/shells to determine the general location of the shooter.
Further, ballistics experts also can match the cartridge/shell to a particular shotgun, handgun or rifle. Cartridge cases are most often identified by breech face, firing pin impressions, extractor, ejector, or chamber marks. A firearm’s breech face rests against the head of the cartridge case and holds the cartridge case in the chamber of the firearm. The firing pin the mechanism of the firearm that strikes the cartridge (primer) to ignite the gunpowder in the round. The extractor is the mechanism that withdraws the cartridge case from the chamber after the firearm has been fired. The ejector is the mechanism that ejects the cartridge from the firearm after it is extracted from the chamber. The chamber is the location where the gun powder is ignited and the bullet is projected into and through the barrel. Each of these parts and mechanisms have unique manufacturing characteristics that combine to make each firearm unique.
Matching a cartridge/shell to a firearm requires comparison of two cartridges/shells. The first from the crime scene and the second would be a cartridge/shell obtained by test firing the firearm. The two cartridges/shells are then compared under a microscope to determine whether they match each other. As scientific as this sounds, even the Association of Firearms and Toolmarks Examiners’ Criteria for Identification Committee acknowledges that this process of identification is subjective based upon an examiner’s training and experience.
As a footnote to this discussion about cartridges and shells, it is important to remember that cartridges and shells can also be an important source of other forensic evidence such as fingerprints and DNA.
There are three types of firearms that are commonly the subject of ballistic examination: rifles, handguns and shotguns. The barrels of rifles and handguns are “rifled,” meaning that parallel spiral grooves that twist to the left or the right are cut into the inner surface (called the bore) of the barrel. As a bullet passes through the barrel, the grooves force the bullet to rotate, giving the bullet stability in flight and increased accuracy. These grooves leave microscopic impressions on the bullet that are used in firearm identification.
Shotguns do not contain these grooves, so it is not possible to identify the projectile with the barrel in this manner.
Rifles and handguns are classified according to the diameter of the barrel of the firearm. This measurement is called the caliber (e.g. .22, .45, .357). Rifles and handguns are also divided into categories based upon the firearm’s loading mechanism. For rifles, the loading mechanism would be semiautomatic, bolt, pump action and lever action. Pistols are either revolver or semiautomatic.
The first step in firearms/ballistic identification is to compare the type of weapon, caliber and rifling characteristics. If a bullet is identified as being a .45 caliber bullet, it could not have been shot from a .22 rifle. Similarly, if a bullet was shot from a firearm with a right twist, firearms with a left twist can be excluded.
If the caliber and rifling characteristics match, then additional testing is performed. The most common test is to perform a test firing of the firearm. This involves firing a bullet from the firearm into a water tank or ballistics gel. This approach allows the examiner to recover the bullet and retain the cartridge from the test. It also insures that the bullet is not damaged during the shot.
The test bullet is compared to the bullet recovered at the crime scene. According to the science, each firearm has unique microscopic barrel characteristics that were created during manufacturing, use of the firearm over time and chemically produced imperfections. If a bullet has the same unique characteristics as the firearm, ballistic identification science considers that to be a match.
As with all science, experts have expressed concern about the scientific reliability of this type of ballistics matching. In 2008 and 2009 reports, the National Academy of Sciences questioned this assumption. Much of the criticism revolved around the lack of standards for determining whether the bullet matched the firearm. According to the 2009 report: “Because not enough is known about the variabilities among individual tools and guns, we are not able to specify how many points of similarity are necessary for a given level of confidence in the result. . . . Individual patterns from manufacture or from wear might, in some cases, be distinctive enough to suggest one particular source, but additional studies should be performed to make the process of individualization more precise and repeatable.” 
Given the concerns surrounding the reliability of firearm identification evidence, a number of criminal courts have prohibited firearm examiners from testifying about to an exact match between a bullet and a firearm.
In Minnesota, it does not appear that the issue of reliability of ballistics identification has been decided by appellate courts. There are a number of cases where the courts have relied upon such evidence, but the scientific reliability of that evidence was not challenged.
Patrick Noaker is an attorney with the Noaker Law Firm LLC who aggressively represents clients in the courtroom, and has presented civil and criminal cases to judges and juries across the U.S. for the past 24 years. Patrick is a former Death Penalty attorney who represents clients in serious criminal cases. Patrick has also handled hundreds of clergy sexual abuse cases in Minnesota and across the United States. Patrick can be reached at his office: 333 Washington Avenue N. # 300, Minneapolis, Minnesota 55401, (612) 839-1080, firstname.lastname@example.org, @Noakerlaw.
 Ian Pepper and Steve Bloomer, Cartridge Casing Ejection Patterns from Two Types of 9mm Self-Loading Pistols Can Be Distinguished From Each Other, Journal of Forensic Identification, Volume 56, Issue 5, September-October 2006, pp. 721 – 725.
 Characteristics of the terrain as well as weapon motion, firearm position and firearm grip also can create significant variability in cartridge/shell location patterns. Lewinski, Hudson, Katrwoski and Redmann, Fired Cartridge Case Ejection Patterns from Semi-Automatic Firearm, Investigative Sciences Journal, Vol,. 2, No. 3, November 2010.
 P. Giannette and E. Imwinkelried, Scientific Evidence 4th Ed., § 14.04.http://www.investigativesciencesjournal.org/article/view/7104/5036
 P. Giannette and E. Imwinkelried, Scientific Evidence 4th Ed., § 14.02.
 Paul Giannelli, Ballistics Evidence Under Fire, ABA Criminal Justice, Volume 25, Number 4, Winter 2011.
 National Research Council, NationalAcademy of Sciences, Strengthening Forensic Science in the United States: A Path Forward 154 (2009).)
 See United States v. Taylor, 663 F. Supp. 2d 1170, 1180 (D. N.M. 2009); United States v. Willock, 696 F. Supp. 2d 536, 546 – 549 (D. Md. 2010), based
 See State v. Meng Vang, 774 N.W.2d 566, 572-573 (Minn. 2009); State v. Goodloe, 718 N.W.2d 413, 418 (Minn. 2006).