Magazine Influence on Cartridge Case Ejection Patterns with Glock Pistols

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1 TECHNICAL NOTE J Forensic Sci, January 2018, Vol. 63, No. 1 doi: / Available online at: onlinelibrary.wiley.com CRIMINALISTICS Wim Kerkhoff 1 ; Ivo Alberink, 1 Ph.D.; and Erwin J.A.T. Mattijssen, 1 M.Sc. Magazine Influence on Cartridge Case Ejection Patterns with Glock Pistols ABSTRACT: In this study, the cartridge case ejection patterns of six different Glock model pistols (one specimen per model) were compared under three conditions: firing with a loaded magazine, an empty magazine, and without magazine. The distances, covered by the ejected cartridge cases given these three conditions, were compared for each of the six models. A significant difference was found between the groups of data for each of the tested specimens. This indicates that it is important that, to reconstruct a shooting scene incident based on the ejection patterns of a pistol, test shots are fired with the same pistol type and under the correct magazine condition. KEYWORDS: forensic science, cartridge case ejection patterns, Glock pistols, magazine influence, shooting incident reconstruction, magazine loading condition In a shooting incident in the Netherlands, a single shot was fired from a semi-automatic Glock pistol after an altercation and fight between two men. The magazine of the pistol had been ejected from the firearm during the scuffle preceding the shot. Establishing the location of the shooter at the time of the shot became important during the legal investigation of the incident. An approximate assessment of the shooter s position was made based on the location of the cartridge case found at the crime scene and on the pistol s cartridge case ejection pattern. At least two sources (1,2) in the literature explicitly or implicitly mention a possible influence of the loading condition of a magazine on cartridge case ejection patterns with automatic and semi-automatic firearms. Taking this information into account, the series of test shots for this particular case were performed without a magazine, corresponding to the witness statements. During the tests, most cartridge cases were not ejected through the ejection port, but fell down through the empty magazine well in the pistol s grip. This result triggered more research, beyond the scope of the case, on the influence of a magazine on cartridge case ejection patterns with Glock pistols. For readers not familiar with Glock pistols, a short introduction on their functioning is given. Glock Pistols In normal use Glock pistols fire cartridge cases from a detachable box magazine, placed in the pistol s grip. One or more cartridges are stacked in this magazine, against the pressure of a magazine spring. After a loaded magazine is placed in the pistol s grip, the slide is pulled back and released. The spring-driven slide rushes forward, picks up the top cartridge from the 1 Netherlands Forensic Institute, PO Box 24044, 2490 AA, The Hague, The Netherlands. Received 27 Jan. 2017; accepted 2 Mar American Academy of Forensic Sciences magazine, and pushes it into the barrel. When the trigger is squeezed, the firing pin strikes the primer in the bottom of the cartridge, which ignites and in turn ignites the powder charge. The powder burns up rapidly, creating a high gas pressure inside the cartridge. The gases push the bullet forward through the barrel. The slide and the barrel, containing the empty cartridge case, move backward due to the reversely directed pressure. After a short travel, the back of the barrel tilts downward, unlocking the barrel from the slide. As the slide travels back further, a part called the extractor pulls the cartridge case from the barrel. During this rearward travel, the cartridge case is in close proximity to, or comes into contact with the top of the magazine and/or the top cartridge in the magazine. After traveling back more, the bottom of the cartridge case hits the ejector. The push of the ejector and pull of the extractor make the cartridge case tumble out of the pistol through a clearing in the slide called the ejection port. After reaching its most rearward position, the slide rushes forward again under spring pressure, picking up the next cartridge from the magazine and loading it in the barrel. This shooting sequence can be repeated as long as there are cartridges in the magazine. After the last cartridge is fired, the slide is held back in the rearward position by a slide stop, indicating to the shooter that the pistol is empty. The slide stop only functions when an empty magazine is present in the pistol s grip. When the magazine is absent, the slide moves forward after a shot. Methods and Materials Firearms and Ammunition Six different Glock pistols of three different calibers were selected for the tests. Per caliber, two models were selected that represent the standard and the shortest available Glock model in these calibers. Table 1 sums up the data of the firearms and ammunition used in the tests. 239

2 240 JOURNAL OF FORENSIC SCIENCES Tested Magazine Conditions Taking the case into account that was mentioned in the introduction, a decision was made to study the influence of the presence and the absence of a magazine. In addition, a decision was made to study the influence of the presence and the absence of a cartridge in the magazine. In summary, the tests were performed under three different magazine conditions: (i) a Loaded magazine, (ii) an Empty magazine, and (iii) an Absent magazine. Shooting Range Set-up and Shooting Position All shots were performed by the same 188 cm (6 0 2 ) shooter, assuming a two-handed position. To help keep the pistol s TABLE 1 Specifications of the used firearms and ammunition Used Glock pistols Used ammunition Model Type Caliber Brand Bullet type Bullet weight 17 Standard 9 mm Luger Winchester FMJ 124 grains 26 Subcompact 22 Standard.40 S&W Magtech FMJ 180 grains 27 Subcompact 21 Standard.45 ACP Remington FMJ 230 grains 30 Subcompact height, position, and direction consistent, the shooter s hand rested lightly against a rod, mounted at a height of 175 cm (5 0 9 ) to the wall of the shooting range. The floor around the shooter was left clear. All shots were fired at a target placed 10 m (33 0 ) in front of the shooter and with the center at a height of 175 cm (5 0 9 ). The shooter aimed at the target for each shot and tried to maintain a firm and consistent grip on the pistols throughout the tests. The shooting range floor underneath the ejection port of the pistol was marked using a plumb bob. An x- and y-axis were applied to the floor, crossing each other at the mark. The y-axis ran parallel to the axis of the firearm; the x-axis crossed it at a 90 angle. Shooting Protocol At the start of each test sequence, the magazine of the pistol to be tested was loaded with two cartridges. The magazine was inserted in the grip and the first cartridge was chambered by retracting and releasing the slide. The shooter assumed the position described earlier and fired one shot. One of two assistants that were present at the shooting range, positioned behind and to the right of the shooter, applied a red sticker, where the cartridge case made first contact with the shooting range floor. As the second cartridge was in the magazine at the moment the case of the first cartridge was ejected, this cartridge case was ejected with the magazine in the Loaded condition. Staying in position and after the red sticker was FIG. 1 Results for the six different Glock pistols. The x-and y-axis depict the position of the cartridge cases first contact on the floor (cm), the origin being the position on the floor underneath the pistol. The red stars denote shots for the Loaded condition, where the magazine contained a cartridge, the blue pluses shots for the Empty condition, and the black dots shots for the Absent condition. [Color figure can be viewed at wileyonlinelibrary.com]

3 KERKHOFF ET AL.. MAGAZINE INFLUENCE ON EJECTION PATTERNS 241 FIG. 2 Distances covered by the cartridges (on the y-axis of the figure) for the three conditions (in the respective three figures) and the six different Glock pistols (on the x-axis of the figure). The distances are illustrated using boxplots. The middle line denotes the median value, the boxes contain the interval from the 25th up to the 75th percentile of the data, and the whiskers reach until the minimum or maximum value found, up to a maximum of 1,5 times the Inter Quartile Range. Data outside this area are denoted by a + symbol. [Color figure can be viewed at wileyonlinelibrary.com] applied, the shooter fired the second shot. The case from this cartridge was ejected with the magazine in the Empty condition. A blue sticker was applied where this cartridge case made first contact with the shooting range floor. After this shot, the shooter fed a third cartridge in the chamber, removed the magazine from the pistol, and fired this cartridge in the Absent condition. A black sticker was applied where this cartridge case made first contact with the shooting range floor. The three-shot sequence described above was repeated 20 times for each of the six tested Glock models. Per tested model, the x- and y-coordinates for each of the red, blue, and black stickers were measured in cm using a tapeline. Results The results for the different Glock pistols and the different shooting conditions (Loaded, Empty, and Absent magazine) are given in Fig. 1. It is clear that for the different Glock models quite different results are obtained. As shown in Fig. 1, for five of the six models tested (all expect model 17) the shots with the magazine absent covered distances (from the pistol) much smaller than the ones with the magazine present (Loaded and Empty conditions). The vast majority of cartridge cases that covered these small distances were observed to drop down through the magazine well. Differences between the shots with an empty or loaded magazine are more difficult to interpret visually. We confine ourselves to the comparison of the shots fired under the three conditions, per Glock model. For ease of exposition, instead of studying the two-dimensional data (x- and y-values), the focus will be on the distances covered by the cartridge cases from the pistol. We start by studying whether the results are different for the different types of Glocks, given each of the three conditions. The distances are depicted in Fig. 2 by means of boxplots. Normality tests were performed on the separate samples, based on the Lilliefors test statistic, cf. (3), and for 4 of the = 18 datasets normality of the distances was rejected. Although three of these are from the Glock 21, it was decided to use nonparametric tests to study differences between observed distances, for all datasets. Differences in distance, per condition, were studied by the Kruskal Wallis test statistic, cf. (4,5). The Kruskal Wallis test (or one-way ANOVA on ranks) is a nonparametric method for testing whether samples originate from the same distribution. Under all three conditions (Loaded, Empty, Absent), the test led to a p-value under This means that under all conditions, the hypothesis of equality of the covered distances over the Glock models is rejected. For the types of Glocks fixed, the distances given the various conditions are depicted in Fig. 3. Differences in covered distances are again studied by the Kruskal Wallis test statistic, differences in standard deviation by the Fligner Killeen test statistic, cf. (6) (the median chi-squared variant was used). In the case of comparison of the three conditions, for all Glock models there is a significant difference between the groups of data, with p-values ranging from (Glock 17) to <10 9 (all other models). As this seems to be caused mainly by the data gathered under the Absent condition, the test statistics were also applied for the comparison of the

4 242 JOURNAL OF FORENSIC SCIENCES FIG. 3 Distances covered by the cartridges (in cm, on the y-axis in the figure) for the six different Glock pistols and the three conditions (on the x-axis in the figure). The distances are illustrated using boxplots, see Fig. 2. [Color figure can be viewed at wileyonlinelibrary.com] Loaded versus the Empty condition. The Kruskal Wallis test yields a significant difference for the Glocks 17 and 21 (p = 0.001, 0.005) and no significant differences (p > 0.05) for the Glocks 22, 26, 27, and 30. With respect to the standard deviation, the Fligner Killeen test yields significant differences (given the two conditions Loaded and Empty) for the Glocks 17, 27, and 30 (p-values are 0.002, 0.001, and 0.016) and no significant differences for the Glocks 21, 26, and 27 (p > 0.05). All in all, the results vary over the different models of Glock pistols. As concerns the distance covered by cartridges, within the same model, for five of the six models it makes a significant difference whether a magazine is present in the pistol or not. Moreover, if interest is in pistols with a magazine present, the distances covered may (the Glocks 17, 21, 27, and 30) or may not (the Glocks 22 and 26) have a different covered distance or standard deviation according to whether the magazine is loaded or empty. Discussion The results confirm the suggestions made by Haag and Haag (1) and Gardner and Bevel (2) about the magazine influence on cartridge case ejection patterns. The cause of the noted influence was not established in this study. It has been noted by Gardner and Bevel (2) that the last cartridge cases ejected from firearms with a slide stop may exhibit different ejection patterns than those of prior nonstopped ejected cartridge cases. As this remark refers specifically to firearms with a slide stop, it implies that the ejection is influenced by the forward moment of the slide. It is this movement that is interrupted by the slide stop, while the prior rearward movement is not. If correct, this theory would explain the differences between the results in the Empty condition and the Loaded condition, as the forward movement is stopped in the Empty condition and uninterrupted in the Loaded condition. It cannot explain the difference between the results in the Absent condition on one side and the Loaded condition, because the slide s forward movement is uninterrupted in both conditions. Another explanation would be that the absence, and/or loading condition of a magazine, has a steering effect on the cartridge case during the rearward movement of the slide. When the cartridge case exits the barrel in its rearward travel, it moves over the top of the magazine toward the ejector. During this movement, the cartridge case might come into contact with the top of the magazine and/or the top cartridge in the magazine when a magazine is present. The contact with the magazine and/ or cartridge might influence the engagement positions of the ejector at the bottom of the cartridge case and of the extractor in the cartridge case rim. It seems plausible that an alternating engagement position of the ejector and/or extractor might influence the direction of ejection. Apart from an influence on ejector and extractor engagement, it is also possible that the magazine or a cartridge applies an upward force on the cartridge case at the moment of ejection. Whether these tendencies are stronger in pistols with a tilting barrel, because the movement of the cartridge case is not parallel to the axis of the firearm but slightly downward, toward the top of the magazine, remains untested. Conclusion The results of this study indicate that it is important that, to reconstruct a shooting incident based on the ejection patterns of a pistol, test shots are fired under the correct conditions. The covered distances of cartridges cases show to differ depending on the condition of the magazine (Loaded, Empty, or Absent). Because only one specimen was tested per Glock model, it is not known whether the noted differences for the three tested conditions are exemplary for the respective models or must be attributed to the individual firearms.

5 KERKHOFF ET AL.. MAGAZINE INFLUENCE ON EJECTION PATTERNS 243 Acknowledgements The authors would like to thank the following persons for their assistance during the tests: Tjeerd van Aalst, Davey van Manen, Laura-Ashley van Dijk, Rene Neijmeijer, Auke Jelle Kampen, Roy Janssen-Bouwmeester. References 1. Haag MG, Haag LC. Shooting incident reconstruction. 2nd rev. ed. San Diego, CA: Academic Press, 2011; Gardner RM, Bevel T. Practical crime scene analysis and reconstruction. Boca Raton, FL: CRC Press, 2009; Lilliefors HW. On the Kolmogorov-Smirnov test for normality with mean and variance unknown. J Am Stat Assn 1967;62: Pestman W. Mathematical statistics, 2nd edn. Berlin, Germany: De Gruyter Textbook, Kruskal W, Wallis A. Use of ranks in one-criterion variance analysis. J Am Stat Assn 1952;47(260): Conover WJ, Johnson ME, Johnson MM. A comparative study of tests for homogeneity of variances, with applications to the outer continental shelf bidding data. Technometrics 1981;23: Additional information and reprint requests: Wim Kerkhoff Netherlands Forensic Institute PO Box AA The Hague The Netherlands w.kerkhoff@nfi.minvenj.nl

REFERENCE PAGE FIREARMS AND BALLISTICS PART 2: CARTRIDGES NAME

REFERENCE PAGE FIREARMS AND BALLISTICS PART 2: CARTRIDGES NAME *A CARTRIDGE is the piece of ammunition placed in a firearm. It is composed of a bullet (the part that is fired through the barrel of the