Measurement of 9 mm cartridge case external temperatures and its forensic application

Abstract

The external temperature of the cartridge cases of 9 mm parabellum ammunition during the firing sequence was measured by a series of methods. Using a thermal imaging camera was the most successful method and showed that aluminium alloy cases reached higher temperatures than did brass cases. Peak temperatures for brass cases were 336 K at the case mouth after 1.2 ms and 331 K at the case base after 2 ms. Corresponding temperatures for aluminium alloy cases were 363 K at the mouth after 0.8 ms and 372 K at the base after 1.2 ms. These times at temperature would not be sufficient to destroy any DNA residues left on the case. Measurement of the DNA of fired cartridges showed that DNA deposited on the cartridge case before firing was not affected by the temperatures reached during the firing sequence. Estimates of temperatures to be found in pure aluminium and mild steel cases were made, these indicating that pure aluminium would give higher temperatures than aluminium alloy and steel a lower temperature than for brass.