Manufacturing of firearms parts: relevant sources of information and contribution in a forensic context

In the context of forensic cases involving firearms, a major issue to address is the identification of the firearm used to discharge questioned elements of ammunition – bullets or cartridge cases – found during the scene investigation. When a questioned firearm is available, reference bullets and cartridge cases are produced through controlled test-fires. The marks left on both the questioned and reference elements of ammunition are analysed before being compared. The processes used to manufacture the firearms tend to influence the type and frequency of some of these marks. Knowing how the questioned firearm was produced is a key element to identify the relevant marks for comparison purposes. Finding this information can be challenging, as it is not necessarily publicly available. After presenting the manufacturing processes used to produce the main parts of firearms in contact with the elements of ammunition, this review includes an updated list of processes used by specific manufacturers, relying not only on the literature. The results highlight the necessity to consider a wide range of sources when gathering information about the manufacturing processes. Apart from general and specialized forensic literature, the online content made available by the manufacturers themselves is also a valuable complementary source of information. Contacting the manufacturers or visiting their premises is sometimes necessary to understand the full extent of the processes and how they can influence the marks of forensic interest

Comparison of three bullet recovery systems

Comparing the marks left on questioned bullets to those left on reference bullets is the main aim of a firearm identification expertise. Thus, producing reference bullets with a questioned firearm is an essential step. Different kinds of system have been developed to safely recover bullets fired from questioned firearms. However, the performance of each system and its impact on traces left on the bullets have not been addressed. Three bullet recovery systems – a horizontal water tank, a cotton tube and a recently designed fleece – were used to fire seven types of ammunition of various type, shape and casing. The bullets were then described and images of their surface were acquired with an automatic system to study the impact of each system on the bullets. The water tank is the more efficient system in terms of quality of the marks. However, it cannot be used to fire every type of ammunition. Some of them, such those used by law enforcement, tend to be damaged with this system. A way to mitigate the problem is to use the cotton or the fleece-based systems, the latter being more universal. It requires a cleaning step to remove all the fibres from the surface of the bullet, but the marks left by the weapon are still of interest

How to recognize the traces left on a crime scene by a 3D-printed Liberator?: Part 1. Discharge, exterior ballistic and wounding potential

The Liberator is a firearm that can be manufactured from its blueprints, using a 3D-printer. This weapon made of nineteen pieces – eighteen in printed plastic and one metallic nail – raises questions such as its ability to fire a round, its wounding potential and the traces produced by its discharge. In particular, knowledge must be gained to infer that a 3D-printed handgun was used, reconstruct the shooting event involving such handgun, and gather information related to the type of 3D-printed handgun used. This study focused on the traces that could orientate forensic investigations when the use of a 3D-printed Liberator is suspected. In a first step, the Liberator was investigated to study its behaviour during the discharge and characterize traces produced by the discharge. To fulfil this goal, some Liberators were printed and assembled. Six Liberators fired a round. The discharge of the weapons was done under specific conditions allowing to collect ballistics data and traces produced by the shooting. The results showed that the barrel tended to break between the ignition of the primer and the moment the projectile exited the muzzle. The speed of the projectiles reached 140 m/s when the barrel broke, while it was about 170 m/s when barrel remained intact. The trajectory of the projectiles was sometimes disrupted, and the projectile tumbled on itself. It was thus very difficult to characterize the trajectory. The cavity wound caused by the fastest bullet was typical of a handgun wound firing a FMJ projectile (penetration of 21 cm in ballistics soap). On the other hand, the cavity caused by the slowest bullet was more representative of a splinter wound (penetration of 14 cm in ballistics soap). The study of gunshot residues collected on adhesive targets showed the presence of unburnt particles and small perforations caused by polymer pieces that concentrated around the entry holes

Was a 3D-printed firearm discharged? - Study of traces produced by the use of six fully 3D-printed firearms

Since the blueprints of the Liberator were published and successfully tested, countless new designs for said 3D-printed firearms and 3D-printed firearm components have been created and made publicly available. These new 3D-printed firearms, which are praised by their designers as ever more reliable, can be found on the Internet with little effort. Press reports have shown that various models of 3D-printed firearms have already been confiscated by law enforcement services around the world. So far, forensic studies have addressed this set of problems relatively little, whereby for the most part only the Liberator has been examined in detail and three other designs were only included a few times. The rapid pace of this development poses new challenges for forensic investigations and unveil new spheres of investigation regarding 3D-printed firearms. This research initiative aims to determine whether the results from previous studies on Liberators, are also reproducible and observable when using other models of 3D-printed firearms. In this respect six fully 3D-printed firearms – PM422 Songbird, PM522 Washbear, TREVOR, TESSA, Marvel Revolver and Grizzly – were produced on a material extrusion type Prusa i3 MK3S using PLA as the material. Test firings of these 3D-printed firearms have shown that they are indeed functional, but that, depending on the model, they suffer different levels of damage when fired. However, they were all rendered inoperative after one discharge and could not be used for further discharges unless the broken pieces were replaced. As in other studies, the firing process and the resulting ruptures on the 3D-printed firearm, projected polymer parts and fragments of different sizes and in different quantities into the immediate environment. The parts could be physically matched, allowing the reconstruction and identification of the 3D-printed firearms. Elements of ammunition also showed traces of melted polymer on the surface and cartridge cases bore tears or swellings

How to recognise the traces left on a crime scene by a 3D-printed Liberator? Part 2. Elements of ammunition, marks on the weapons and polymer fragments

The Liberator is a firearm that can be manufactured from its blueprints by the means of a 3D-printer. This handgun is composed of nineteen pieces: eighteen made of printed polymer and one metallic nail. This study focuses on the physical traces which can be found and exploited from a forensic point of view after the discharging of such types of pistols. Two main aspects have been investigated: (1) whether it can be inferred that a 3D-printed handgun was used when investigating a scene; (2) when presuming the use of a 3D-printed Liberator on a scene. Six Liberators were manufactured, assembled and discharged. The discharge occurred under controlled conditions to allow the collection of ballistics data and traces produced by the shooting. Elements of ammunition – cartridge cases and projectiles – that were fired during an experimental campaign appeared to carry polymeric materials (flakes, melted polymer or both). Besides, we observed that the fired ammunition elements lacked traditional marks left by the metal pieces of a conventional firearm. Indeed, the projectiles did not carry rifling marks and the cartridge cases were found torn or swollen. Fragments or larger pieces of polymer were found, mostly on the ground, near the location of the discharge, up to nine metres away. The impression of the cartridge case head stamp was also found on a part of the Liberator called the “hammer body”. This study showed that the discharge of a 3D-printed Liberator is expected to produce traces that can be transferred onto and recovered from the printed firearm, the cartridge case, the projectile, the target, and the environment of the discharge. These traces are different from those left by conventional firearms. When found on investigation scenes, some of these traces can inform on the use of a 3D-printed handgun and contribute to the reconstruction of a shooting event involving such a weapon. This study suggests that the approach adopted when investigating a scene must be adapted in terms of traceology when the use of such firearm is suspected

Influence of the printing process on the traces produced by the discharge of 3D-printed Liberators

Since its introduction in 1986, 3D printing technology is in constant development. 3D printers are becoming more and more performant and accessible. In 2013, the Liberator blueprints are released online. This single-shot pistol can be entirely manufactured using a 3D printer, except for the firing pin and the ammunition. First, this research aims at establishing an overview of all the elements and traces potentially present when a 3D-printed firearm is involved, whether it is fired or not. In the second part, we study these elements for exploitability to obtain information about the manufacture of the firearm (printing processes, 3D printers and polymers). For this purpose, a total of 36 Liberators were manufactured using different printing conditions (i.e., printing processes, printers, polymers and parameters). The tested printing processes were based on the principles of Material Extrusion (ME), Vat Photopolymerization (VP) and Powder Bed Fusion (PBF). All 3D-printed firearms manufactured via ME and PBF were able to fire whereas Liberators manufactured by VP printing could not be fired. This could be explained by the lack of precision of the prints making it impossible to assemble some of the Liberators, or by the fact that the polymer was not suitable to produce the springs. All the barrels were broken by the discharge, projecting polymer pieces or fragments into the environment. These polymer pieces or fragments were examined to determine which printing process was used as well as other elements related to printing parameters and conditions (e.g., layer height, filling pattern and infill density). This information is useful to determine whether a certain command file, slicer or 3D printer could be at the source of a questioned 3D-printed firearm. Melted polymer or polymer particles on elements of ammunition may also be present after the firing process. However, the examination of these particles does not allow inferring other information, except the possible use of a 3D-printed polymer firearm.N/