Cartridge Cases Research Articles

Time since contact influences DNA profiling success of cartridges and fired cartridge casings

Forensic DNA analysis of cartridges and fired cartridge casings remains challenging, possibly due to the heat and pressure generated during firing of the weapon as well as metal ions from the casings that have been suggested to initiate DNA degradation and inhibit PCR during the DNA profiling process. Even though recently developed DNA recovery protocols have shown to significantly improve DNA yields and DNA profile success rates no information is available on whether the time interval between contact and the DNA recovery process has an influence on these outcomes. In the current study 40 cartridges and 40 fired cartridge casings were left untreated for 24 h or 1 week after which the rinse-and-swab technique was used to collect DNA. Higher DNA yields and higher DNA profile success rates were obtained from cartridges compared to fired cartridge casings. The same general observation was made when cartridges and fired cartridge casings were processed after 24 h compared to after 1 week. In addition, DNA profiles suitable for comparison could still be generated from samples when real-time PCR quantification indicated DNA concentrations < 0.001 ng/μl, suggesting that quantification results may not be reliable when assessing the presence of DNA on such items. In conclusion, the results indicate that cartridges and fired cartridge casings should be processed for DNA profiling as soon as possible and that DNA quantification results should be interpreted with caution as DNA profiles suitable for comparison could be missed.

Preliminary investigations using Recover Latent Fingerprint Technology on unfired ammunition and fired cartridge cases

Previous studies have identified the potential benefit of the disulfur dinitride (S₂N₂) process to operationally relevant substrates. However, the majority of this work was conducted on prototype equipment that had substantial differences to the commercialised system (Recover Latent Fingerprint Technology (LFT)) in terms of design and chemical delivery. This paper evaluates the performance of Recover LFT on a problematic exhibit encountered within a fingerprint enhancement laboratory: unfired and fired ammunition. Three pseudo-operational experiments involving non-groomed, naturally handled fingermarks were conducted on the most commonly encountered types of ammunition used in crime in the United Kingdom (UK). In addition, Recover LFT was compared against Superglue Fuming followed by Basic Yellow 40 (BY40) Fluorescent Dye Staining (a commonly used alternative) to ascertain if the process provides added benefit to fingermark recovery rates. The results show that fingermark visualisation on small calibre cartridge cases remains difficult with few marks achieving enough ridge detail for comparison. However, this paper also shows that the novel Recover LFT process, which is still in its infancy and requiring optimisation, is no worse than currently implemented visualisation processes and is therefore worth further investigation.

Classification of fired cartridge cases using 3D image capture and a comparison of database correlation method performance.

When firearms are used, they leave unique marks on the fired bullets and shells. Examining these marks gives clues about the crime scene and the weapon of the crime. However, due to the increase in the number of incidents in which firearms are used, the increase in the amount of evidence makes ballistic investigations very difficult and prolongs the analysis time of the evidence. With the automatic image analysis and identification system, ballistic evidence can be examined very quickly and used to classify possible matching evidences. In this study, we present an approach based on Image Similarity Measurement for forensic examination of cartridges from automatic pistols. For this purpose, we used 500 images of 9 × 19 mm and 500 images of 7.65 × 17 mm cartridge cases obtained from 20 different brands and models of pistols. We divided the images of bullet cartridges into four different categories as breech face, firing pin, ejector mark, and combined evaluation, and we obtained these images from the BALİSTİKA 2010 system. We investigated the classification and matching performance of the obtained four category images using 4 different methods: Structural Similarity (SSIM), Root Mean Square Error (RMSE), Peak Signal to Noise Ratio (PSNR), and Universal Image Quality Index (UQI). The results show that our Structural Similarity (SSIM) approach is effective in classifying and matching ballistic evidence.

Comparison of four commercial solid-phase micro-extraction (SPME) fibres for the headspace characterisation and profiling of gunshot exhausts in spent cartridge casings

Headspace solid-phase micro-extraction (SPME) is a promising technique for the characterisation and profiling of gunshot exhausts in spent cartridge casings, especially for health and environmental risk assessments, as well as forensic purposes. To date, however, no comprehensive investigation has been carried out to objectively assess the kinds of compound released during a discharge that can be recovered by this approach, the selectivity of the main commercially available fibres, and their relative performances for the analysis of gunshot exhausts and the discrimination of different ammunition types. This study aimed to fill this gap. Gunshot exhausts in spent cartridge casings from four different ammunition types were analysed by GC–MS, after extraction with four different commercial fibres: 100 μm polydimethylsiloxane (PDMS), 85 μm polyacrylate (PA), 65 μm polydimethylsiloxane/divinylbenzene (DVB), and 85 μm carboxen/polydimethylsiloxane (CAR). Results showed that, overall, a total of 120 analytes could be observed across the cartridges, but the different tested fibres also displayed distinct performances, which were, to some extent, complementary for the characterisation of gunshot exhausts. DVB, in particular, recovered the most compounds simultaneously. On the other hand, the observed variability between measurements was also high, making it a poor candidate for (semi-)quantitative applications (e.g. estimation of time since discharge and/or source profiling). In this regard, PA demonstrated the highest potential for broad use and implementation in multi-purpose methods.

Некоторые вопросы оценки влияния приборов для бесшумной стрельбы на образование следов на выстреленных пулях и стреляных гильзах

Introduction. The growing number of military and civilian models of firearms equipped with muzzle devices actualizes the expert diagnostics of the facts of using silent shooting devices during committing crimes by their traces on the fired bullets and fired cases. Theoretical analysis. Science has identified a number of regularities of the effect of silent shooting devices on the mechanism of formation and characteristics of traces on bullets and cartridge cases. Among them are the abrasion and smoothing of traces of the barrel bore on bullets, the formation of traces of the body of homemade silent shooting devices when they are misaligned with the barrel bore, the malfunction of the weapon’s automation, which excludes the possibility of displaying traces of the reflector and the ejection port on the cartridge cases. Empirical analysis. In order to identify new regularities of influence of silent shooting devices on the formation of traces on bullets and cartridge cases, a model scientific experiment was conducted. Experimental shooting was conducted from .366 TKM smoothbore rifles models VPO-209 (Paradox) and AK-366 (Lancaster). The PBS-1 with a rubber obturator of a strong degree of wear was used as a silent shooting device. Cartridges of two types were equipped with lead bullets in a polymer shell, gunpowder “Sunar 7.62” and “Falcon”. Results. It is determined that lead bullets of cartridges undergo characteristic deformation when passing the rubber obturator of the silent shooting device. The body of the bullets stretches and bends, in some cases takes a spindle shape. Cases of partial destruction of bullets have been noted. It is proved that the smoothing of the relief of the traces of the barrel bore, characteristic of the contact interaction of a bullet with a rubber obturator, as well as the additional formation of obturator traces on the bullets do not prevent the identification of firearms. Conclusions. The identified regularities expand the possibilities of forensic ballistic examination in determining the facts of the use of silent shooting devices while committing crimes.

Идентификационный период самодельного огнестрельного оружия

Introduction. Currently, cases of illegal use of homemade firearms are increasingly common in expert practice. When examining the scene of the incident, experts seize bullets and shells fired from homemade pistols and revolvers. While examining them, databases of traces are created. Possible reasons for the difference in the identification period of homemade firearms from factory ones are discussed. Experiment. To establish the identification period in homemade firearms, experiments were carried out, during which a significant difference was found between the identification period of homemade firearms and factory-made firearms. Discussion of the results. When studying the dependence of maintaining the individualizing complex of features unchanged in traces on bullets and cartridge cases, it was revealed that the identification period of homemade firearms is much shorter than that of factory-made firearms, which must be taken into account in expert practice.

Особенности идентификации оборудования релоадинга по следам на переснаряженных гильзах

Introduction. In connection with legalization of autonomous cartridges loading to the rifled firearm, the matter of forensic examination of reloaded cases is growing more urgent. Aims and tasks. To examine the regularities of trace formation made by the reloading equipment on reloaded cases in order to identify the method of making cartridges, whose parts they have originally been, and to establish the fact of reloading by means of the same production mechanisms. Experimental part. Examination of the traces formed in the course of a shot and reloading was carried out with hunter’s .300 win mag caliber cartridge cases ejected from .300 win mag caliber Sauer 202 carbine. The following reloading equipment was used: manual threaded (single-stage and turret) presses produced by Neck, threaded molding matrices produced by Redding. Discussion of results. Reloading equipment is considered as a production mechanism depositing traces on the surface of the reloaded cases. In the case of identification (selecting a group of objects from a multitude, determining their group belonging) the structural features of their cutting surfaces, their traces being imprinted on the processed parts, are studied. As a whole, they are suitable for identifying the instrument that formed them. Defects in trace-forming objects (matrices, shellhorder, etc.) can also be seen in the traces on the cases as subclass features. These features can be taken into account in the comparative study of cases to establish the fact of reloading using the same production mechanisms.

Recovery of DNA from fired and unfired cartridge casings: comparison of two DNA collection methods

For over 10 years, various studies have attempted to increase the recovery of DNA from ammunition by modifying the DNA collection, extraction, purification, and amplification procedures, with varying levels of success. This study focused on the “soaking” method of Montpetit & O’Donnell [1] and the “rinse-and-swab" method of Bille et al. [2]. First, testing for the presence of exogenous DNA, 210 boxed cartridges (brass, steel, and nickel-plated) from nine manufacturers were swabbed and DNA was extracted, concentrated, and quantified. Extracts that quantified > 0 ng/µL (44 of 210) were amplified and genotyped with GlobalFiler™. Of those, only one extract yielded two alleles indicating that the manufacturing and packaging of ammunition was virtually DNA free. Next, to obtain a baseline comparison of two DNA collection methods on a non-metallic substrate and identify a suitable number of cells to spot on cartridges, different DNA input amounts of primary human adult epidermal keratinocytes (HEKa) were tested. Thereafter, 300 brass and 300 nickel-plated, cartridges were spotted with HEKa cells containing ~5 ng of DNA, fired or unfired, and processed with either method. Finally, five methods representing hybrids of the soaking and rinse-and-swab methods were tested to determine if variations of those methods could be used to increase DNA yield and recovery. The results show that the soaking method consistently yielded more DNA than the rinse-and-swab method from a non-metallic substrate. However, the comparison study demonstrated that both methods performed comparably for cartridges. On average, the soaking method recovered 0.25 ng of DNA (5.1% recovery) and the rinse-and-swab method recovered 0.28 ng (5.8% recovery). However, average recoveries were significantly different among three analysts and considerable variation in yields were observed, possibly due to storage time. Furthermore, consistent with prior reports, the DNA recovered from brass casings was only 16% of that recovered from nickel-plated casings and the average yield of DNA from fired casings was reduced to 67% of unfired casings. Moreover, DNA extracts from brass or nickel-plated casings did not appear to contain amplification inhibitors and only 30/596 appeared severely degraded. Finally, both the published rinse-and-swab and soaking methods yielded more DNA than all modifications of the two methods. Overall, both methods yielded equivalent DNA quantities. Additionally, recovery of DNA from any given cartridge casing may be dependent on storage time as well as the skill, proficiency, and experience of the analyst and may reflect stochastic effects, particularly for casings containing low copy and/or degraded DNA.

Encapsulated sleeve with high reliability and short response time for sniper rifle cartridges

The article provides data on the new design of encapsulated cartridge case for sniper cartridges for high-precision sniper complexes. The encapsulated sleeve is considered as a device, the change in the design and parameters of which significantly change the reliability of the operation of sniper cartridges of high-precision sniper complexes. The design of the proposed capsule sleeve and the method of manufacturing a three-lobed anvil for this sleeve are protected by patents of the Russian Federation. The design of a sniper cartridge with this sleeve is also proposed, which allows to unify the size of the capsular socket for various brands of sniper cartridges. The results of field tests of the new design of the encapsulated sleeve are presented.

Particle image velocimetry for velocity measurement of muzzle flow: Detailed experimental study

A deep understanding of muzzle flow fields is essential for optimizing muzzle devices and projectile design. This flow characterization has been heretofore limited to local and intrusive measurement techniques such as pressure measurements using pencil probes. Consequently, the quantitative experimental data are limited, so are the number of numerical codes validated in this field. The objective of the present work is to demonstrate the applicability of the Particle Image Velocimetry (PIV) technique to provide accurate velocity measurements in the challenging environment of the propellant flow of a .300 blackout weapon. During this work, we have studied the feasibility of PIV on the muzzle flow using: (i) the naturally existing particles in the combustion gas as tracers, (ii) two different solid tracers; namely TiO2 and ZrO2 particles with a nominal size of 100 nm, seeded using two different methods. The first method implies coating the propellant grains with the tracer powder, in the second one the tracer is added directly inside the cartridge case. The experiments aim to demonstrate in particular: (i) the capability of PIV to resolve the main structures of the flow, (ii) the assessment of particle response across the Mach disk, and (iii) the non-alteration of the weapon's ballistics. To achieve this goal, an experimental setup with five different measurements was installed: (i) PIV system, (ii) classical high-speed schlieren visualization, (iii) optical particle counter, (vi) pressure transducer in the combustion chamber, and (v) projectile velocity measurement. The experimental results demonstrated (i) the ability of PIV to accurately resolve the main features of the flow as well as the instantaneous velocity field; (ii) that the combustion products contain sub-micrometric particles which can follow with high fidelity the gas flow; (iii) that solid ZrO2 particles, when coated on the propellant grains, are suitable as tracers presenting a good flow fidelity and that the seeding of these inert particles is recommended in subsonic conditions (or whenever there is a lack of unburned particles); and (iv) that the TiO2 particles intended to act as tracers, surprisingly not only melted but also functioned as a combustion accelerator and decreased the number of particles in the propellant gas.

Composition optimization and characterization of combustible cartridge cases with polyvinyl acetate (PVAc) as a binder

Combustible cartridge case samples composed of nitrocellulose (NC), polyvinyl acetate (PVAc), kraft cellulose (KC), dibutyl phthalate (DBP) and diphenylamine (DPA) were prepared to study their structures and chemical and mechanical properties. Taguchi’s experimental design method was used to design the experimental formulations. First, simultaneous thermogravimetry-differential scanning calorimetry (STA TG-DSC), scanning electron microscopy (SEM), Brunauer–Emmett–Teller analyser (BET), bomb calorimeter (BC), vacuum stability tester (VST) and a tensile testing machine (TTM) were employed to analyse the thermochemical characteristics, structure, explosion heat, chemical stability and compatibility, and mechanical strength of all formulated samples. Based on the analysis results, the weight loss of the combustible cartridge case sample obtained by the TG experiment was chosen as the quality characteristic. The results of the Taguchi analysis indicated that the optimal parameter combination was an NC/KC weight ratio of 80:20, an NC/PVAc weight ratio of 85:15, an additional DPB of 3.5 wt.% and a density of 1.25 g/cm3. The results of the chemical stability and compatibility test, explosion heat test and mechanical strength test show that the test samples prepared with the optimal parameter combination can meet the requirements of combustible cartridge cases. Furthermore, the combustion performance of the combustible cartridge case sample prepared with the optimal formula was measured by a high-temperature combustion furnace (HTCF) and burning rate measurement device (BRM). The experimental results indicated that the autoignition temperature and ash content were 231 °C and 0.28%, respectively. In addition, the burning rate increased with increasing combustion chamber pressure but was lower than that of ordinary gun propellants at the same pressure. These combustion characteristics can meet the quality requirement of combustible cartridge cases. Finally, an actual combustible cartridge case was prepared and verified. The result of the performance verification test indicated that the average ash content was 0.30%, which was similar to that of the previous test samples and met the quality requirement.

Influence of Thermomechanical Treatment on the Microstructure and Mechanical Properties of Cu-28Zn-4Mn Alloys

Cartridge case ammunition is made from brass alloy by deep drawing process with high degree of deformation. For this reason, the material with a good formability, strength, and hardness is required. The improvement of mechanical propeties of the brass alloy can be conducted by severe process such as addition of alloying element and also termomechanical process. The purpose of this study is to determine the effect thermomechanical processing by cold rolling process with 70% thickness reduction followed by annealing process with variation temperature of 400°C, 500°C and 600°C for 30 minutes to the microstructure and mechanical properties of Cu-28Zn-4Mn alloy. The samples of Cu-28Zn-4Mn alloy were produced by gravity die casting process by using the ingot of Cu, Zn as well as the Mn powder as the feeding materials. The investigation results show that thermomechanical prosess change the microstructures of Cu-28Zn-4Mn alloy. The cold rolling process with 70% thickness reduction will convert the equiaxial grain into an elongated structure (shear band). Furthermore, the heat treatment by annealing process will return the microstructure from elongated to equiaxial grain. Thermomechanical process also tends to change mechanical properties. The 70 % cold rolling process increases the hardness of the Cu-28Zn-4Mn alloy. The hardness of as homogenized and 70% cold rolled samples are 62.34 VHN and 103.96 VHN, respectively. Further, the annealing process tend to decrease the tensile strength and hardness of Cu-28Zn-4Mn alloy. Tensile strength of Cu-28Zn-4Mn after annealing process with variation of 400°C, 500°C, and 600°C are 355.13 MPa, 299.16 MPa, and 294.79 MPa, respectively. On the other hand, the hardness of Cu-28Zn-4Mn with the same treatment are 91.84 VHN, 71.76 VHN and 67.46 VHN, respectively. In contast, the annealing process tend to increase the elongation value. The samples elongation after the annealing process with variation of 400°C, 500°C, and 600°C are 25%, 28%, and 30%, respectively.

Towards the protection of ammunition headstamps during fingermark enhancement processing; a preliminary study

Forensic recovery from fired ammunition casings remains one of the most challenging tasks during high-profile investigations. Often, the decision must be made between screening for DNA or fingerprints, and, in doing so, the impact these processes will have on the examination of ballistic markings imparted on the ammunition from the firearm itself. Traditionally, fingermark enhancement processes have yielded low success rates in their efforts to identify suspects by enhancing friction ridge detail left on the cartridge casings. Moreover, the enhancement methods utilised may often induce detrimental physical changes to the casing(s), rendering them unsuitable for subsequent ballistics (marking) examination. Recently, new technology has been shown to increase the success rate of fingermark recovery from fired ammunition, and the growing adoption of such innovation means that new challenges are encountered to maximise evidence recovery and streamline forensic workflows. One such example arises from the potential obscuration of the ammunition headstamp area during such treatments. Accordingly, this study outlines the preliminary investigations and developments of a polymer mask substrate that serves to protect the headstamp of fired ammunition casings during relevant fingermark enhancement processes. The technique also has the capacity to be used as a surface protection device to eliminate unwanted chemical deposition across other areas of interest and evidence types.

Approach to breech face impression comparison based on the robust estimation of a correspondence function

Forensic firearm analysis concerns an attempt to determine if ammunition is associated with a specific firearm based on tool-marks produced by it. A feature-based method using the Scale Invariant Feature Transform (SIFT) and RANdom SAmple Consensus (RANSAC) integration algorithm had been suggested to allow the automated comparison of breech face impressions. In this paper, an estimation method is proposed to establish a correspondence function among the features of comparison impression pairs, aiming to further improve the robustness and repeatability of automated feature matching. During the application of the iterative establishment algorithm, the Support Vector Regression (SVR) method is repeated to estimate the correspondence function based on current feature correspondences, and a robust weighting method excludes egregious outliers among putative correspondences by updating additional weightings. Moreover, the consistency detection method is adopted to overcome the over-fitting problem in SVR. Validation tests of the proposed method are conducted on three sets of cartridge case’s breech face impressions; namely the Fadul set consisting of 40 cartridge cases ejected from 10 Ruger P95PR15 pistols, the Weller sets containing 95 cartridge cases obtained from 11 Ruger P95DC firearms and the Lightstone set containing 30 cartridge cases from 10 SW40VE S&W Sigma pistol slides. Test results show that most known matching (KM) pairs possess no less than 20 matching feature points while the non-matching (KNM) pairs all maintain 3–8 correspondences. It also indicates that the feature-based method has apparent advantages in dealing with granular impressions with local peaks and valleys features, and poor performance on the striation marks. The clear distinction between KM and KNM impression pairs demonstrates the feasibility of the proposed method in ballistic feature comparison. Compared to the random hypothesize-and-verify modeling of RANSAC, this method can retain more reliable matching feature points of the impression pair to ensure the repeatability of feature correspondence selection.

Improvement in High Temperature‐Resistant Performance and Waterproof Property of Combustible Cartridge Case with BEMS Resin Based Composite Coating

AbstractCombustible cartridge case (CCC) is an important charge component which is very suitable for the weapon systems that need light load. It is a kind of nitrocellulose‐based porous material which has a low ignition temperature and strong hygroscopicity. Thus, if the surface of the CCC is not protected very well when it is used in modern weapon with faster fire rate, it will be easy to self‐ignite in the high‐temperature gun barrel and absorb moisture in a high‐humidity environment. These problems will worsen both the safety of gun operators and the combustion performance of CCC. However, they are not solved well by current research and industrial practice. Herein, we designed a new composite coating which can improve both the high temperature‐resistant performance at a higher temperature and waterproof property of CCC. The boron nitride (BN) and epoxy resin were used to modify silicone resin. The BN and epoxy modified silicone (BEMS) resin, inorganic adiabatic fillers and other additives were mixed together to prepare a BEMS resin based composite coating solution, and then the solution was sprayed on the surface of the combustible cartridge case to form a protective coating. The chemical structure of BEMS resin was investigated by FTIR. The thermal stability of coating films was analyzed by TGA. The high temperature‐resistant performance, water contact angle on the surface and waterproof property of the coated CCC were analyzed by muffle furnace experiment, water contact angle tester and immersion test, respectively. Results show that boron nitride and epoxy resin were successfully grafted on silicone resin chains. Compared with control samples, the thermal decomposition rate of the prepared coating films is significantly reduced. The coated CCC will keep 108.8 seconds while not burning at 230 °C. The heat resistant time increased by 16.74 % at 230 °C. The water contact angle on the surface of the coated CCC can reach 105.71° which was improved by 67.01°. After being soaked for one hour, the water absorption of the coated CCC is reduced by 96 % in distilled water and by 99 % in 3.5 wt % of sodium chloride solution. Compared with most present coatings, the new BEMS resin based composite coating which we designed can improve both the high temperature‐resistant performance and waterproof property of the CCC significantly and effectively. It provided a new way for study on the protective coating of CCC.

Deep Learning Based Classification of Military Cartridge Cases and Defect Segmentation

The final stage of the production process in the industry is quality control. Quality control answers the question of is there a defect on the surface of the products. Frequently the quality control is performed manually. The disadvantages of manual quality control are high error rate (low accuracy), low product rate (low performance) and high expense rate (high cost). The solution is automatic quality control using machine vision systems. These systems classify the products and segment the defects on their surfaces by processing the images taken by cameras during the production process in real-time. Some products like military cartridge cases have metallic, cylindrical, non-uniform texture and highly reflective surface. So, the quality of images is very important. Another factor that affects the accuracy is the non-uniform texture of the product surface. Distinguishing the product non-uniform texture from defect texture is a challenging problem. In previous works, this problem have been tried to be solved with image processing and deep learning techniques and the accuracy of 97% and 96% have been obtained, appropriately. According to NATO standards, the accuracy of the classification of the military cartridge cases should be above 99%. In this work, the methodology for classification of the military cartridge cases and segmentation of the defects on their surfaces with non-uniform texture is proposed to increase the accuracy. In scope of the proposed methodology the datasets with non-defective, defective and labeled/masked image classes of the cartridge cases were created, the deep learning models to classify the military cartridge cases and segment the defects on their surfaces were proposed, implemented and obtained results were evaluated using the metrics such as Accuracy, Precision, Recall, F1-Score, Jaccard Index (JI) and Mean Intersection over Union (mIoU). Obtained results showed that the proposed methodology increased the accuracy of classification to 100% with the DenseNet169 model and the F1-Score of segmentation to 92.1% with Improved U-Net and ResUnet models.

Planning, design and logistics of a decision analysis study: The FBI/Ames study involving forensic firearms examiners

This paper describes design and logistical aspects of a decision analysis study to assess the performance of qualified firearms examiners working in accredited laboratories in the United States in terms of accuracy (error rate), repeatability, and reproducibility of decisions involving comparisons of fired bullets and cartridge cases. The purpose of the study was to validate current practice of the forensic discipline of firearms/toolmarks (F/T) examination. It elicited error rate data by counting the number of false positive and false negative conclusions. Preceded by the experimental design, decisions, and logistics described herein, testing was ultimately administered 173 qualified, practicing F/T examiners in public and private crime laboratories. The first round of testing evaluated accuracy, while two subsequent rounds evaluated repeatability and reproducibility of examiner conclusions. This project expands on previous studies by involving many F/T examiners in challenging comparisons and by executing the study in the recommended double-blind format.

Forensic comparison of fired cartridge cases: Feature-extraction methods for feature-based calculation of likelihood ratios

We describe and validate a feature-based system for calculation of likelihood ratios from 3D digital images of fired cartridge cases. The system includes a database of 3D digital images of the bases of 10 cartridges fired per firearm from approximately 300 firearms of the same class (semi-automatic pistols that fire 9 mm diameter centre-fire Luger-type ammunition, and that have hemispherical firing pins and parallel breech-face marks). The images were captured using Evofinder®, an imaging system that is commonly used by operational forensic laboratories. A key component of the research reported is the comparison of different feature-extraction methods. Feature sets compared include those previously proposed in the literature, plus Zernike-moment based features. Comparisons are also made of using feature sets extracted from the firing-pin impression, from the breech-face region, and from the whole region of interest (firing-pin impression + breech-face region + flowback if present). Likelihood ratios are calculated using a statistical modelling pipeline that is standard in forensic voice comparison. Validation is conducted and results are assessed using validation procedures and validation metrics and graphics that are standard in forensic voice comparison.

Surveying practicing firearm examiners

A sample (n = 79) of practicing firearm and toolmark examiners was queried about casework as well as their views about the potential role that statistics might play in future firearm examinations and expert witness testimony. Principal findings include: The modal response for time spent conducting bullet examinations is 2–4 hours, and the modal response for cartridge casings is 1–2 hours. The average participant (median) makes an identification in 65% of casework, makes an elimination in 12% of casework, and reports that the examination was inconclusive in 20% of casework calls. The vast majority of examiners work at laboratories that permit eliminations when class characteristics agree. The reported industry-wide false positive error rate is 1%, though very few participants could name a study or give a citation for their reported estimate. Qualitative responses about the potential role of statistics were mixed.

Cold stamping of a cartridge case blank for 40x53 mm caliber grenade launcher ammunition

Problems. The choice of a rational method for stamping blanks with two hollows is usually carried out according to the permissible degree of deformation, the coefficient of material utilization, and the productivity of the process without taking into account the effect of the deformation pattern on the final mechanical properties of the stamped semi-finished product.&#x0D; Purpose of the study. Determination of a rational method for stamping a blank of a 40x53 mm grenade launcher cartridge case based on the results of computer modeling using the finite element method. Cartridge case material - AD35 aluminum alloy. The workpiece has two hollows with different diameters and depths.&#x0D; Implementation technique. By means of computer modeling using the finite element method, two options for stamping of a workpiece are researched - double-sided extrusion and sequential reverse extrusion with tilting of the workpiece.&#x0D; Research results. Based on the results of the research, the features of deformation according to the given schemes, as well as the energy-force parameters and parameters of the stress-strain state of the processes, are determined. It has been established that both methods make it possible to obtain blanks with specified geometric dimensions. At the same time, sequential back extrusion provides a more uniform and predictable deformation of the material along the cross-section of the workpiece, but loses in productivity to double-sided extrusion.&#x0D; Conclusions. The obtained research results can be used as criteria when choosing the optimal option for stamping of a workpiece with two hollows by cold extrusion.