A study of gunshot residue distribution for close-range shots with a silenced gun using optical and scanning electron microscopy, X-ray microanalysis and infrared spectroscopy

Effect of mounting a sound suppressor on distribution and total amount of inorganic gunshot residue on targets

Sound suppressors critically modify barrel overall length and ballistic performances of hosting guns and are therefore expected to influence the patterns of the plumes of gunshot residues (GSR) reaching the targets. Despite the forensic interest, in recent years, a single paper was published on the variations induced by the use of a suppressor in the spatial distribution of visible soot clouds on close targets and in the number of a few selected classes of GSR particles detected by scanning electron microscopy. A different approach, based on x-ray fluorescence (XRF) and inductively coupled plasma-optical emission (ICP-OES) spectroscopies, that points to most of the metallic elements ejected from the barrel, is suggested here. The confirmed effect of a sound suppressor up to a distance of 20 cm is to gather the cone of particles reaching the target. Despite this pattern modification, the global concentrations of the ammunition-related elements of interest (Pb, Ba, Sb, Cu) on targets cannot be considered significant (i.e., with 95% confidence) reduced by the use of a suppressor, due to the high intra-specimen and inter-specimen ICP-OES data dispersions. Differently, the hypothesis of a role of homemade suppressors in enriching GSR populations in Fe is supported by our results. The presence of iron is indeed the only indication of the actual use of a suppressor, a piece of information that is useful for the correct interpretation of the lead patterns visualized on targets for muzzle-to-target determination.

Investigation of the impact of a sound suppressor on the weapon's memory effect and gunshot residue formation

The firearm's memory effect describes circumstances where particles from previous firing cycles are deposited with or incorporated in the new ammunition debris. Even though this phenomenon is well studied, the influence of a sound suppressor on the strength of the memory effect and its extent has not yet been investigated. In this study, the SINOXID-type ammunition barium, antimony lead with added aluminum (BaSbPbAl) primer mixture, was initially fired, followed by firing ammunition with classic SINOXID primer composition BaSbPb. Thirty bullets were test fired with and without a suppressor, accompanied by sample collection in predetermined shooting intervals. The results of the present study demonstrate that the memory effect was significant even after 30 shots of the latter classic SINOXID ammunition, both with a suppressed pistol or unsuppressed pistol, and that the proportion of the particles not compatible with the primer composition was unequivocally pronounced when using a suppressed pistol. Moreover, shooting a suppressed pistol affects the total amount of gunshot residue found on the shooter's hands; thus, it should always be considered in reconstructions of shooting incidents. Explanations for this phenomenon are offered.

Gunshot Residue Deposition With and Without Firearm Suppressors (Silencers)

ABSTRACT

Forensic pathologists recognize the importance of estimating the range of fire for gunshot entrance wounds. Classically described ranges of fire include contact, close range, medium (or intermediate) range, and indeterminate (or distant) range. The presence or absence of gunshot residue (smoke/soot and/or gunpowder) and the characteristics of the gunshot residue are evaluated in order to estimate the range of fire. It is well known that interposed targets can block or otherwise alter gunshot residue deposition. In this preliminary study, a comparison is made between gunshot defects produced on targets using firearms with and without an attached suppressor device (so-called "silencer"). Comparisons are made at various distances from the targets, using multiple weapon/ammunition calibers.

Organic and inorganic gunshot residues on the hands, forearms, face, and nostrils of shooters 30 min after a discharge

During the investigation of firearm-related incidents, gunshot residues (GSR) can be collected on the scene and individuals (e.g., shooters or bystanders). Their analysis can give valuable information for the reconstruction of the events. Since GSR collection on persons of interest generally occurs a few minutes to hours after discharge, knowledge is needed to understand how organic (O), and inorganic (I) residues are transferred and persist. In this research, the quantities of OGSR and IGSR were assessed on the right and left hands, forearms, face, and nostrils of four shooters. Specimens were collected immediately before the discharge (shooter's blank specimens) and shortly after (30 min) using carbon adhesive stubs. Organic compounds were first extracted from the collection device and analysed using ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Subsequently, IGSR particles were detected on the same stub using scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDS). Shooter's blank specimen analysis revealed background contamination of both O and IGSR in the shooter's environment, predominantly attributed to the presence of an indoor shooting range. However, the background quantities generally remained below the associated 30-minute specimen. Thirty minutes after a discharge, higher quantities were generally detected on the shooter's right and left hands than on other collection regions for both GSR types. Forearms and face emerged as interesting collection alternatives, especially in cases where a person of interest may have washed their hands in the interval between the discharge and collection. In contrast, very low amounts of GSR were detected in the nostrils. Furthermore, the results indicated that OGSR and IGSR have different transfer and persistence mechanisms.

Chemical Analysis of Gunpowder and Gunshot Residues

The identification of firearms is of paramount importance for investigating crimes involving firearms, as it establishes the link between a particular firearm and firearm-related elements found at a crime scene, such as projectiles and cartridge cases. This identification relies on the visual comparison of such elements against reference samples from suspect firearms or those existing in databases. Whenever this approach is not possible, the chemical analysis of the gunpowder and gunshot residue can provide additional information that may assist in establishing a link between samples retrieved at a crime scene and those from a suspect or in the identification of the corresponding model and manufacturer of the ammunition used. The most commonly used method for the chemical analysis of gunshot residue is scanning electron microscopy with energy dispersive X-ray, which focuses on the inorganic elements present in ammunition formulation, particularly heavy metals. However, a change in the legal paradigm is pushing changes in these formulations to remove heavy metals due to their potential for environmental contamination and the health hazards they represent. For this reason, the importance of the analysis of organic compounds is leading to the adoption of a different set of analytical methodologies, mostly based on spectroscopy and chromatography. This manuscript reviews the constitution of primer and gunpowder formulations and the analytical methods currently used for detecting, characterising, and identifying their compounds. In addition, this contribution also explores how the information provided by these methodologies can be used in ammunition identification and how it is driving the development of novel applications within forensic ballistics.

A study of dispersion of gunshot residue from a frequently used Serbian ammunition cal. 7.65 mm to support selected aspects of casework in North Macedonia

The subject of this research was the inorganic gunshot residue component collected from shooting patterns obtained on woven cotton cloth using a Pietro Beretta model 70 pistol, cal. 7.65 mm and Serbian ammunition for the following muzzle-to-target distances: 25, 50, 75, 100 and 125 cm. For each distance, three rounds of shooting were performed. Particles were lifted within a 10 cm radius of the projectile entrance and automatically analyzed using a scanning electron microscope coupled with an energy dispersion X-ray spectrometry. The obtained data on the populations of particles were analyzed taking into account their numbers, chemical classes and sizes. The results showed an apparent maximum incidence within all particles containing barium at about 50 cm distance. Also, lead particles revealed a distinct behaviour, being dominant at a 25 cm distance, falling below the other chemical classes, and finally becoming dominant again at 125 cm. The analysis of the frequency of occurrence of particles sorted according to their sizes confirmed that the small particle population is the largest, and their distribution in function of the equivalent circle diameter is exponential-like. The obtained results provided knowledge on the distribution of particles in the vicinity of the tested firearm and ammunition cal. 7.65 mm which generally corroborates with similarly studied GSR distributions obtained for the use of pistols cal. 9 mm. This information, together with the examinations of gunshot damages and other types of residues such as soot or unburned propellant grains may support qualitative inferences on shooting distance estimation, especially in cases, when the firearm and cartridges are not available to perform test shooting. In such cases even roughly estimated shooting distance can be helpful, e.g. for confirming or excluding the possibility of self-inflicted injuries or suicide and infer on the mutual position of the shooting stage actors. An example of casework that illustrates intermediate shooting distance estimation is presented.

Effects of the interaction of gunshot residue plume and cotton fabrics—an empirical study towards extensive assessment of close-range shooting distance

This study is focused on the distribution of gunshot residue as well as changes in the textiles to support forensic investigations of suicides and homicides committed by means of a firearm.

Combustion Performance of Spherical Propellants Deterred by Energetic Composite Deterring Agents

In order to achieve ideal burning progressivity and reduce harmful phenomena such as muzzle flame and smoke, energetic composite deterring agents (ECDAs) deterring spherical propellants were designed and prepared. The combustion performance of ECDA-deterred propellants was characterized by a closed vessel, and the interior ballistic performance was studied by a ballistic gun. High-speed photography and a smoke box were employed to capture muzzle flames and smoke. The results showed that triethylene glycol dinitrate (TEGDN) had a slight deterring effect weaker than that of poly(neopentyl glycol adipate) (PNA) on the propellants. The maximum pressure in the closed vessel bore of the ECDA-deterred propellants was 2.29 MPa higher than that of the dibutyl phthalate (DBP)-deterred propellants, though the L-B curve of the ECDA-deterred propellants was slightly lower and its combustion time was 0.44 ms longer. For ECDA containing 5 wt % PNA and 3.2 wt % TEGDN, 80 °C and 150 min are the best deterring conditions. The average velocity of the bullet propelled by ECDA-deterred propellants was increased by 93.4 m·s^-1, while the average maximum pressure in the gun bore was decreased by 19 MPa, compared with the original propellants. The muzzle flame and smoke of the ECDA-deterred propellants were significantly reduced compared with the DBP-deterred propellants, where the smoke concentration was reduced by up to 44.5%.

Interpol review of gunshot residue 2016-2019

This review paper covers the forensic-relevant literature in gunshot residue analysis from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

Screening of Gunshot Residue in Skin Using Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Hyperspectral Microscopy

The detection of gunshot residues (GSR) in skin is important in criminal forensic investigations related with firearms. Conventionally, the procedure is based on the detection of metallic or inorganic residues (IGSR). In this work, we propose attenuated total reflectance Fourier transform infrared (ATR FT-IR) hyperspectral microscopy as a complementary and nondestructive technique for detection of organic GSR (OGSR). The spectra were acquired from GSR of three ammunition manufacturers, which were collected from shooter's hands by the tape-lifting method. Before spectroscopic analysis, a Na-Ca bleach solution was added to all GSR samples on the tape for destroying skin debris. Positive detection of OGSR spectra were achieved by ATR FT-IR hyperspectral microscopy. Spectra show characteristic patterns of nitrate ester compounds which agrees with the propellant chemical composition. Characteristic ATR FT-IR spectral patterns of OGSR were measured from visualized GSR particles demonstrating the potential of ATR FT-IR hyperspectral microscopy.

Force and Sound Pressure Sensors Used for Modeling the Impact of the Firearm with a Suppressor

In this paper, a mathematical model for projectiles shooting in any direction based on sensors distributed stereoscopically is put forward. It is based on the characteristics of a shock wave around a supersonic projectile and acoustical localization. Wave equations for an acoustic monopole point source of a directed effect used for physical interpretation of pressure as an acoustic phenomenon. Simulation and measurements of novel versatile mechanical and acoustical damping system (silencer), which has both a muzzle break and silencer properties studied in this paper. The use of the proposed damping system can have great influence on the acoustic pressure field intensity from the shooter. A silencer regarded as an acoustic transducer and multi-holes waveguide with a chamber. Wave equations for an acoustic monopole point source of a directed effect used for the physical interpretation of pressure as an acoustic phenomenon. The numerical simulation results of the silencer with different configurations presented allow trends to be established. A measurement chain was used to compare the simulation results with the experimental ones. The modeling and experimental results showed an increase in silencer chamber volume results in a reduction of recorded pressure within the silencer chamber.