The mechanical study of the launching, flight, behavior and effects (usually visual marks) of bullets is what ballistic fingerprinting usually refers to. The forensic procedure is used to identify the gun with which the criminal fired, thus being one step closer to identifying the murderer. The analysis is concentrated on the marks that the firearms leave on the bullet, which – just like fingerprints – are unique and the study of the trail refers to internal ballistics (the analysis of the mechanical processes between the moment of firing and the one in which the bullet leaving the barrel) applied on forensic matters (the implication of legal questions, investigations and situations subject to the law).
There are numerous techniques that the forensic ballistic specialists use during the investigative process. The first and most obvious ones concern gross differences between the physical qualities of the firearm and the bullet. For instance, a bullet of 10 mm could have never been fired through a 9 mm barrel. While there is little expertise needed for this first procedure and it may look common-sensical, it really reduces the range of possibilities and makes the fire-gun easily accessible and identifiable. This easy kind of comparison is only meant to help the law enforcement agents proceed to the next steps of ballistic fingerprinting.
Striations are highly important during the forensic investigations, since every barrel has different ones, depending on numerous factors (among which the most important are the type of fire-gun, the tear level, the spin rate). The consequences of these barrel characteristics that can be deduced from the bullet (for instance, the twist to the left instead of a twist to the right – visible on the bullet marks – can lead to characterizing the barrel, which is a major step in the procedure of gun identification). Following these characteristics of the bullet can lead, if not to the gun itself, to another series of reductions on the trailing and back-tracking, which can help identify the fire-gun, along with the other procedures and evidence of the case that is analyzed.
The marks on the bullets depend on the types of rifling in the barrel, which at their turn are divided into two main categories: class characteristics – varying on the manufacturer and model of the fire-gun, different in shape and number of grooves, direction and twist rate. They can reduce the list of suspected fire-guns, but they’re not self-sufficient for the identification process. The individual characteristics on the other hand are produced by deformities and imperfections of the rifling process and its afferent tools. Another common cause for the imperfections that cause the individual characteristics of the rifling is represented by wear and tear in the regular use, reason for which they can suffer changes due to time factors. The most informed criminals (or simply citizens who do not agree with the government’s intrusion measures in their private life) customize and try to alter the individual characteristics of a gun, the most common methods being the abridgment or the changing of the barrel, or using a steel brush to friction the interior of the barrel.
Using breech markings on the cartridge case is another efficient method of identifying the weapon, due to the marks that can be matched to the breech and chamber. There are several reasons for which it is much easier to identify cartridge cases than the bullets, the most important being the durability and the resistance of the cartridge. While the bullet tends to suffer transformations after the impact, the cartridge will still be usable in identifying the type and size of the gun, thanks not only to the durability on the impact, but to their own individual markings that will not alter with time and usage. Whenever there are situations in which the hammer was switched out or worked on, the significance of the hammer striking the case becomes highly relevant to the identification process.
While the all in all procedure is highly effective for manual guns, there are some errors of tool. The first and most important one is that the identification process cannot trace back a shotgun, since most of the times there’s a protective plastic sleeve on the bullet making it resistant to the traces tha the barell would normally mark it with.
Another problem of this identification method is that there is no national/international database of the fire-guns. There have been numerous debates, especially in the United States of America, where the gun control represents a national issue of the moment, that there should be special national databases with the ingerprints. The only city to have applied this measure, however, is Maryland, where a fired case from the firearm has to be taken to the Maryland State Police where every new firearm will be photographed in order to log the information on a database. There is a report written by the police station of Maryland concerning this procedure to disband this idea, since the expenses are not justified and the database did not help in any criminal case.
The second (and more popular) solution is the bullet marking procedure, which has had several proposals in the United States of America, on different national and confederate levels. Some of the jurisdictions have even passed the legislation to the effect. The most popular proposal is firearm micro-stamping, procedure by which the make, model and serial number of the gun is engraved both on the cartridge and on the face of the firing pin, which leads to the stamping of the primer while the firing pin impacts.
In 2008 there was a British researcher who proposed to the ammunition manufacturers coating the bullets of the fire-guns with pollen (or pollen deposit) coated with metal oxide. Since the pollen is highly difficult to be completely washed off, the attachment to the clothing and hands of criminals would only mean extra forensic evidence on the case, while the main advantage would consist of the hard outer case of the pollen grains, that would help them survive being fired. Using unique combinations of these chemicals and some other ones would make the ballistic fingerprinting easily traceable. A national poll held in the same year as this research was made showed that 77% of the citizens of the United States of America would agree with laws sustaining the ballistic fingerprinting, which would help the police identify what gun fired which bullet.
Ammunition serialization is another measure that was proposed as an alternative law enforcement tool that would facilitate the investigations of ballistic fingerprinting, gaining serious amounts of time on each investigation, given the fact that identifying the gun is the first step on finding the criminal, and not the final one.