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FIRED CARTRIDGE CASE EJECTION PATTERNS FROM

SEMI-AUTOMATIC FIREARMS

 

 

 

 

The scatter plot shown in Figure 3 more precisely illustrates the randomness of the landings of spent cartridge casings not only within the entire 360 degrees surrounding the shooter, but also in each individual quadrant. This can be seen in the distance the spent cartridge casings landed from the zero point. The minimum distance the spent cartridge casings traveled from the zero point was 3.61 inches (9.17 cm) while the farthest distance was 253.40 inches (643.64 cm) with an average of 80.93 inches (205.56 cm). The difference from the average distance to the maximum distance is then over 14 feet (4.27 m). Both the fact that over a quarter of all the spent cartridge casings landed outside the area most often cited by experts and the distance the cartridge casings landed from the zero point illustrates how using the placement of a single spent cartridge casing to determine shooter location is not as precise as it may seem.

Weapon Position and Grip

 

Researchers have cited both the position the weapon was held and the grip of the weapon during firing as important variables in using spent cartridge casing ejection patterns in a shooting reconstruction (Hueske, 2006; Haag, 2006). The following tests fixed firearm position and accounted for different grips for all the firearms used in this study, but it still showed significant variability in spent cartridge casing locations. For example, the results shown in Figures 3 and 4 show a normal firearms position and grip for trained police officers, while Figures 5 and 6 involved a one-handed grip and irregular firearm position. The results shown in the previously listed figures and tables are the results obtained for all firearms used in the study.

 

Figure 4 shows the percentage of spent cartridge casings in each 30 degree section for test 1, a two handed correct grip. This is the standard position in which police officers are trained to shoot. Shown in this figure is that 97 % of the spent cartridge casings landed in the three 30- degree sections to the right and rear of the shooter even when eight different semi-automatic weapons were tested. The reader can see that accounting for firearm position and grip but not firearm motion, type, or ammunition further confirms that most spent cartridge casings land to the right and rear of the shooter. However, this also once again leaves some of the spent cartridges casings unaccounted for in another quadrant and again does not consider dispersal within the quadrant as a significant factor.

 

The scatter plot (Figure 5) presents a much more compact dispersion of spent cartridge casings than in Figure 2. This confirms that firearm position and grip does contribute to spent cartridge casing ejection patterns for this study. Having both of these variables accounted for gives greater strength to the possibility that a spent cartridge casing ejected from these firearms, held in a tradition fashion, will land to the right and rear of the shooter like other experts say it should. Variability within the individual quadrants, however, still remains large. This can be seen in test one (Table 2) with all firearms present by the minimum, maximum, and average distance the spent cartridge casings traveled from the zero point. The minimum was 22.36 inches (56.79 cm); the maximum distance was 230.22 inches (584.76 cm) with an average of 93.88 inches (238.46 cm).

 

Summary information from test 1 with all firearms can be found in Table 2. Variability is once again illustrated in spent cartridge casing ejection patterns even while controlling for certain variables.

Test six involved holding the firearm with a one handed grip pointed 22 degrees downward and cantilevered 45 degrees inward. Changing the firearm position as in this condition drastically changed the spent cartridge casing pattern from that seen in Figure 4 above. In this case, for all firearms, only 29.2% of the spent cartridge casings landed to the rear and right of the shooter and each of the 30-degree sections had some cartridge casings land in them (Figure 6). This illustrated the impact that firearm position and manipulation of the firearm by the shooter has on spent cartridge casing placements.

The scatter plot (Figure 7) illustrates the diversity of spent cartridge casing locations in all four quadrants versus a concentration in quadrant four as seen in Figure 4 above. Once again variability in the individual quadrants was found. For this test the spent cartridge casings landed a minimum distance of only 3.61 inches (9.17 cm) and maximum of 165.41 inches (420.14 cm) from the zero point. The rest of the information obtained from test 6 with all firearms is summarized in Table 3 below. As more and more variables are taken into account the reader can see what an impact they can have on the spent cartridge casing patterns. In this section we can observe that just changing the firearm position alone across all the firearm types and ammunition dramatically influenced the spent cartridge casing pattern observed.

Firearm Type

 

Firearm type is another variable that should to be taken into consideration with shooting reconstruction (Hueske, 2006; Haag, 2006). Eight different semi-automatic firearms were used over the course of this study. When limiting experimental variables to only one type of firearm, the Glock 17, and one firearm position, the standard one, the following results for the ejection patterns were found.

 

Figure 8 illustrates the spent cartridge casing variation found when using only one firearm, one test position, and no firearm movement. It is then expected that this test with a firm correct grip on the firearm and no motion should result in the most compact distribution of spent cartridge casings the reader has seen so far. Our results indicated that almost 50% of the spent cartridge casings landed in one 30-degree section to the right and to the rear of the shooter while 81% (an additional 31%) landed in two 30-degree sections to right and rear. However, 7.5% of the spent cartridge casings landed outside of the quadrant to the right and rear. This is greater than the 3 % (Figures 4 and 5) of the spent cartridge casings ejections that were found outside of quadrant four when firearm type was not accounted for.

 

The scatter plot (Figure 9) shows the actual spent cartridge casing locations for the Glock 17. The minimum distance traveled by the spent cartridge casings from the zero point was 22.36 inches (67.64 cm) and the maximum was 157.97 inches (401.24 cm). This is almost two feet (.6 m) from the shooter at a minimum and over thirteen feet (3.96 m) at a maximum. While a rather compact dispersion was found in quadrant four it is important to remember the variability found here in the difference between the minimum and maximum distances when using only one spent cartridge casing to determine shooter location.