The average weight of propellant in each group was recorded; the results are contained in Table 5.2. The chemical composition of each brand of cartridge was determined by GC/MS. The TICs are shown in Figure 5.1, and the data are summarised in Table 5.3 to aid analysis.
Table 5.2. The average weight of the propellant from 5 types of 12 bore shotgun ammunition
Group Average weight of propellant
1 1.380 gm
2 1.217 gm
3 1.329 gm
4 1.400 gm
Figure 5.1. GC/MS analysis of unfired shotgun cartridges
Analysis of the data in Table 5.1 shows that each brand of ammunition contained three or more substances of the seven components listed in Table 5.3. The following bar charts (Figures 5.2-5.6) depict the relative concentration of each constituent within the smokeless powder. The absolute concentrations in the unfired cartridges are irrelevant as these will change dramatically upon firing.
Table 5.3. The present components in each group of unfired shotgun ammunition
Ammunition 2.4-DNT 2.6-DNT DPA EC DBP 2-NDPA 4-NDPA
Group 1 X X X X X
Group 2 X x X X X
Group 3 X X X
Group 4 X X X X X X
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Figure 5.2. Bar chart of detected compounds in Group 1 ammunition
Figure 5.4. Bar chart of detected compounds in Group 3 ammunition
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Figure 5.6. Bar chart of detected compounds in Group 5 ammunition
The bar charts clearly show that there are notable differences in composition depending upon the brand of shotgun cartridge. While this study is limited to only five brands and samples of three cartridges for each brand, it is clear that the differences have the potential to identify brands based on their chemical compositions.
5.2.5 Discussion
In general, smokeless shotgun powders are composed of nitrocellulose (NC) (i.e. they are single-base propellants). Therefore, it is necessary to dissolve the nitrocellulose pellets using an appropriate organic solvent in order to release the organic components.
The combination of GC/MS was used for the analysis of organic materials in GSR. GC allows for rapid and sensitive separation of the mixtures while MS provides identification of the resulting peaks from the chromatogram [14].
Gas chromatograph is not an ideal technique for the analysis of non-volatile materials such as nitrocellulose. In this study the nitrocellulose, which is the major component, was ignored and the analysis focused on the minor components which provide a means of determining the origin (brand) of shotgun cartridges.
Identification of a bullet that has been used by matching it to a batch of ammunition is not possible based on its physical characterisation and visual inspection. Likewise, it is not possible to predict smokeless powder composition based on the calibre or bullet type [225]. However, since each ammunition manufacturer has its own unique chemical
composition of the smokeless powder [107]. The discrimination between different types of small arms ammunition can be achieved by the presence or absence of certain organic compounds in smokeless powder [226].
In this study, the analysis of the smokeless powder samples was achieved by determining the constitution of each brand and comparing the result with the compounds that were detected in each group.
The composition of each brand of ammunition analysed contained three or more substances of the seven components mentioned in Table 5.3; DPA, 2-NDPA and 4-NDP were found to be the most common compounds detected in all groups.
DPA is the most frequent stabiliser used in smokeless powder, particularly in single base powder. In addition, the main reaction products of nitrous oxide gases and DPA are 2-nitrodiphenylamine, 4-nitrodiphenylamine and n-nitrosodiphenylamine [30]. The addition of the stabiliser to the smokeless powder has the effect of slowing down the decomposition of nitrocellulose, by removing the nitrous and nitric acids that are produced [30].
Most of the components detected in Group 1 were 2,6-DNT, 2,4-DNT, DPA, 2-NDPA and 4-NDPA. In contrast, most of the organic compounds that were found in Group 1 were found in Group 2. DBP is used as a plasticiser in smokeless powder to maintain powder shape during the manufacturing process by improving flexibility [14, 220]. It is widely used in products other than smokeless powder. Therefore, the presence of DBP alone has lower value in forensic science. On the other hand, the combination of DBP with EC, MC, and DPA adds further certainty that the unknown samples being analysed are smokeless powder [227].
Lyalvale Express - “world cup” was the only smokeless powder in which ethylcentralite (EC) was detected. The presence of EC in this group even at trace level can be used as indicator to identify the type of manufacturer that i.e. Lyalvale express-“world cup”. It is common to use EC as a stabiliser and burning rate moderator in smokeless powder, but rare to find it in a normal environment, thus it is considered to be credible organic GSR [29].
There are some similarities between the compounds that were found in all groups, which may be attributable to the number or type of organic compounds, although some
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differences in the concentration of these compounds were noted from one group to another. The degree of variation in the concentration of smokeless powder additives could be interpreted to varying amounts of these additives in the propellant [107, 228]. This gives further evidence that each brand may contain different concentrations of the main constituents. In general, results showed that there is a similarity in the components of the propellant that was made from the same manufacture.
From the results, no NG or MC was detected in any type of ammunition. The absence of NG may be an indication of the type of smokeless powder that was used (i.e. single- base propellant). However, NG is commonly found in the environment, particularly in certain pharmaceutical preparations. Notably, no methylcentralite was detected in any types of ammunition. That could be due to the place of powder manufacture.
It could be possible to discriminate between ammunition based on the concentration of their chemical compositions. GC/MS results confirmed that it is possible to distinguish between different types of ammunition based on the organic compounds in the propellant.