Determination of Firing Distance based on Pellet Dispersion

Research Article

Austin J Forensic Sci Criminol. 2023; 10(1): 1094.

Determination of Firing Distance based on Pellet Dispersion

Kostorrizos A¹*; Spiliopoulou C²; Moraitis Κ²; Papadodima S²

¹Hellenic Police, Firearm & Toolmark Examiner, Greece

²Department of Forensic Medicine and Toxicology, School of Medicine, University of Athens, Greece

*Corresponding author: Athanasios Kostorrizos Firearm & Toolmark Examiner, Former head officer of the Firearms & Tool Marks Section, Hellenic Police Forensic Science Division, Athens, Greece. Email: [email protected]

Received: May 05, 2023 Accepted: June 07, 2023 Published: June 14, 2023

Abstract

According to literature, practice and experience, the firing distance from shotguns (i.e., the distance between the victim and the muzzle of the gun) can be determined fairly accurately by studying and evaluating the pellet dispersion pattern after shooting a target surface, either on clothing or on the victim’s body. Many formulas have been published in order to determine the range at which a shotgun has been discharged, as well as the parameters that affect the calculation of the estimated firing distance. Τhe purpose of the current study was to provide answers to questions regarding firing distance ranges, by firing 12-gauge shotguns from 10, 18 and 25 meters, using different sizes of barrel choke and pellet sizes. Experimental shots were fired from two different guns, with different technical characteristics, from different distances and with different types of shotshell charges. The research revealed that 65% to 80% of the pellet pattern is distributed evenly in the center of the shot and this percentage remains the same at all three distances (10, 18 and 25 meters). Also, an important term in research is Shotgun Pellet Pattern (SPP), which is based on the number of pellets that are uniformly imprinted in the center of the shot and is an important factor in determining shot distance. The results of the shootings were recorded in tables and integrated into a computer program, giving useful information to the case examiner regarding the ability to determine the firing distance from a shotgun.

Keywords: Shotgun pellet pattern; Firing distance; Pellet dispersion; Range estimation; Distribution pattern; Shotguns

Introduction

When a shotgun is fired, the pellets come out of the muzzle of the barrel as a rapidly moving compact mass. As the muzzle of the shotgun is moved further from the body, the diameter of the entrance wound increases in size, until a point is reached where individual pellets begin to separate from the main mass. At close range shooting, shotguns are considered the most dangerous and deadly of all small arms. The lethality of a shotgun wound depends on the number of pellets that enter the body, the organs hit by the pellets, as well as the amount of tissue destruction [1]. The pellet dispersion on a target surface and its correlation with the distance depends on many factors. Some of these include the type of shotgun, the barrel length, the extent of choke, the shotshell pressure and the conditions of the physical environment. Different degrees of choke will result in different patterns for a particular shotgun charge and range. The severity of the injury caused by a shotgun - as a variable of the distance between the victim and the gun - can be classified into a four-level severity scale (Type 0, Ι, ΙΙ, ΙΙΙ), that is based on the pellet pattern, and correlates with morbidity and mortality rates [2].

Firing distance estimation is one of the most valuable elements in the cases of shotgun injury, and especially in cases of homicide, due to the way pellets disperse as the shot range increases [1]. The forensic scientist is responsible for determining the distance of the shot, thus, they should be present throughout all stages during the investigation of the crime scene, so that they can estimate the exact distance of the shot, while also considering the autopsy findings. In order to determine the firing distance accurately, one needs to know as much information as possible about the case, and especially about the technical characteristics of the shotshells used. The ballistics experts should know every piece of information recorded in the autopsy report, and all details related to the circumstances of the shooting, when examining a shot pattern. Das and Singh, focused on the effect of barrel length, choke, shotshell loading and firing distance on the distribution of pellets, placing particular emphasis on what ballistics examiners must know when examining a shot pattern [3]. In their study, Rios, et al, were measured the shotgun pellet dispersions, using a shotgun with the parameters: barrel length, discharge distance, choke constriction and shot size. They found, using statistical analysis between dispersion and the parameters examined no association for shot size or barrel length, and little for choke. Distance being the only large correlation with dispersion [4]. The model which presents, Nag and Sinha explain the natures of the dependence of dispersion on firing distance as well as on gun-ammunition parameters, which are essential for a faithful reconstruction of a crime scene. The model has been tested with such experimental data as are available and reasonable agreement is observed [5].

The present study aims to provide additional information for determining shot distance based on the study of pellet dispersion on a target surface. Due to problems in determining the firing distance in cases where the shotgun is fired from a long distance, i.e., over 15 meters approximately [1] (in which scenario the dispersion of the pellets on a target surface – or on the victim’s clothes or body – may not produce an accurate picture of the possible firing distance, since a number of pellets would not have hit the target surface or the victim), the present research has been carried out from various distances, namely from 10, 18 and 25 meters. Cakir et al. in their own study used a 12-gauge caliber shotgun, without a degree of barrel constriction, with a barrel length of 52cm and shot sizes of 2, 3, 5 and 8mm, at shooting distances of 0.7, 0.8, 0.9, 1, 2, 3, 5, 10, 20 and 25m, for experimental shots. They were attempting to determine the shooting distance based on the pattern of the distribution of pellets, and they subsequently discovered a significant correlation in regard to each pellet size [6].

Materials and Methods

Current Method

The only reliable method of determining range is to obtain the actual weapon, as well as the same brand of ammunition used, and then conduct a series of test shots to reproduce on paper the fatal wound pattern [1]. The first step includes test shots from different distances with a shotgun and shotshells of the same technical characteristics used in the crime committed, and comparative analysis with the pellet pattern of the shooting incident. In the second step, if the shotgun has not yet been found, but the technical characteristics of the shotgun shotshells are known, test shots are fired from different distances with different shotguns, but with shotshells with the same technical characteristics as those ones used in the shooting incident. Afterwards, several test shots are fired in order to reproduce on the test paper the pattern of the shooting incident. In the absence of the shotgun or the shotshells used, test shots should be fired with various shotguns, and a comparative analysis between these shots and the ones on the target surface or on the victim’s clothes, or on the victim’s body of the person targeted in the crime, must be conducted in order to make assessments and draw conclusions.

In their study, Arslan et al. showed that the distribution of pellets on a target surface depends on factors such as the type and caliber of the weapon, the length and diameter of the barrel, the degree of choke, the type of the gunpowder and the loading of the shotshell, as well as the environmental conditions that were present at the time of the shot [7]. Maitre et al. demonstrated the importance of the distance between the barrel of the firearm and the victim, as well as the degree of the barrel’s narrowing (choke) in shaping the distribution of pellets, in relation to the length of the barrel weapon that seems to affect the dispersion of pellets to a lesser extent [8]. The pellets’ size, weight and type, the wad type, as well as the design and loading of the shotshell, are also factors that should always be considered when estimating the degree of dispersion [9].

At closer ranges, firing distance evaluation based on pellet dispersion can be complemented by gunshot residue pattern analysis (via specific chemical tests) or by other characteristics (tattooing, blackening, burning, buffer and wadding impact marks). In order to resolve any issues that may arise in regard to determining the firing distance when using shotguns from distances of 10, 18 and 25 meters, a total of 144 test shots were fired for the present study. At these distances, the shotgun dispersion pattern has no other characteristics that could be used to determine the firing distance. This method included all possible combinations of weapons, shotshells and firing distances.

Shotguns, Shotshells, experimental conditions and test fires

Shotguns (Table 1 & Table 2)