Spent cartridge cases

When a bullet leaves the muzzle of a firearm there is recoil in the opposite direction to the travel of the bullet. Although the recoil is a nuisance it can be used to eject the spent cartridge case, load a live round of ammunition, and cock the mechanism. This can also be achieved by using some of the gas generated during discharge. 

As a result of the need to reuse spent cartridge cases for economic reasons, there has been no mercury in U.S. military small arms primers manufactured since 1898. It was used to a later date (about 1930) in certain U.S. commercial primers. In 1898 the U.S. military adopted a nonmercuric primer composition, coded H-48, for use in the. 30 Krag cartridge. The primer composition was ... 

Comparison macroscopy of spent bullets and spent cartridge cases... 

Identification of weapon types from spent cartridge cases and spent bullets... 

Type of gun—A low success rate for FDR detection has been observed for casework involving. 22 caliber revolvers and rifles, and for shotguns which are usually closed breech weapons, some rifles, namely, bolt action, require manual extraction of the spent cartridge case consequently the design of the firearm can have an influence on the quantity of FDR deposited. 

The interior of spent cartridge cases were sampled by dry swabbing with 0.25 g of acrilan fiber for FAAS analysis (dry swabbing) or by double-sided adhesive tape (Scotch pressure sensitive tape) on the end of a suitable diameter... 

Figure 19.1 Residue in spent cartridge case (blanks).

The classification scheme is based on discharge residue particles from modern primed brass-cased ball ammunition. It is only applied rigidly when no other information is available. When a gun, ammunition, spent cartridge case, or bullet is recovered, it can be examined to determine elemental composition and likely discharge residue particle composition. 

In previous casework in which the majority of the FDR particles contained potassium and sulfur, frequently at high levels, it was thought that the ammunition responsible probably contained black powder. In most of the cases the type of ammunition was not known, whereas in others the sampling and analysis of the residue from the interior of the spent cartridge cases confirmed the presence of black powder. 

The interior of the spent cartridge case is routinely examined whenever FDR is detected on a suspect, to determine the type of primer involved in the incident. Figure 21.1 and Figure 21.2 illustrate primer types as determined by FAAS and SEM/EDX examination, respectively. 

A detailed summary of primer types encountered over a 13-year period (1975 to 1987) is given in Table 21.4 which represents the examination of 1,300 spent cartridge cases, involving 310 different head stamps and 58 manufacturers, and is based on casework results, some of which are included in Figure 21.1 and Figure 21.2 and Table 21.3. 

The fact that the spent cartridge cases in Table 21.4 were not analyzed for potassium or chlorine to indicate potassium chlorate makes interpretation difficult. Nevertheless, Table 21.4 does support the history of primer development as outlined in Chapter 9. 

Spent cartridge cases, originating from the same ammunition type, were examined to determine the amount of mercury remaining in the cartridge case. Results are given in Table 22.5. 

Table 22.5 Mercury Remaining in Spent Cartridge Case...

Average results indicate that approximately 24% of the mercury remains in the spent cartridge case/primer cup, approximately 7% of the mercury was recovered from the liquid traps, and only 1.5% of the mercury was present on the filter. Approximately 68% of the mercury appears to be present as large particulate matter, which must have been deposited on the interior of the firing tube. 

The mercury concentration remaining in the spent cartridge case was considerably higher than previously experienced. This test did not reproduce the conditions experienced during the discharge of a round of ammunition, where much higher temperatures and pressures are attained, plus the possible suction effect in the wake of the bullet. To simulate actual conditions a further test was devised (Figure 22.2). 

Averaging the results it would appear that in the region of 6.60 pg of mercury exits via the breech (ignoring spent cartridge case), of which approximately 48% is particulate (approximately 40% was retained on the filter). 

Loss of Mercury from Spent Cartridge Cases... 

The suspect may have been standing close to a discharging firearm, may have picked up a recently discharged firearm, may have cleaned a firearm, may have picked up spent cartridge cases, may have had contact with the target, and so forth. However, the presence of FDR does demand an explanation from the suspect. As FDR could be present from nonfirearm sources, for example, cartridge-operated tools, occupational/environmental sources need to be considered. 

Firearms and their associated ammunition, spent bullets, and spent cartridge cases provide useful information for identifying suspects, terrorist groups, and the criminal history of a weapon. Unfortunately, despite the numerous detailed books on the physical aspects of firearms, very little has been published on the chemical aspects, and what has been published is sparse and fragmented. 

A particular firearm could be active over many years in terrorist hands and may or may not be recovered. A link report is a report that connects two or more shooting incidents by comparison macroscopy of spent cartridge cases and/or fired bullets, and we were frequently required to provide such reports for court purposes. This often involved a large amount of work. In one particular case 605 spent cartridge cases and 46 spent bullets had to be examined, and in addition to the 27 original reports a further 19 link reports were required for court purposes. 

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