To understand the particular sonic signature of the shot that killed Nawara and Abu Daher – live ammunition fired through a rubber bullet extension – it was important to make more comparative analyses. In order to understand the effect of the rubber bullet extension on the sound of live fire, spectrographs were produced of live ammunition fired through M16 rifle without any extension mounted on the barrel. We then made spectrographs to compare the muting effect of a silencer in comparison to the suppression effect of a rubber bullet extension on the sound of M16 live fire. Through doing this we learned that the rubber bullet extension reduces the muzzle blast noise in a similar, if reduced capacity, to that of a silencer.
- M16 rifle live fire without any extension mounted on the barrel
- M16 rifle live fire with silencer mounted
- M16 gunfire comparison
Above is a spectrographic illustration of four shots: the first is live fire; the second is live fire through a rubber bullet extension; the third is rubber bullet fire; and the last is live fire through a silencer. Three key things can be deduced from this comparative analysis.
- The rubber bullet example (the 3rd shot) is most distinct in that it is the only shot that does not make any sound in the high frequencies from 18khz and above. All the live fire examples occupy, even if faintly, the full frequency spectrum shown.
- In the lower frequencies at 1khz and below, the two shots with extensions mounted (shot 2 and shot 4) greatly reduce the intensity of noise from the muzzle. Even still, the rubber bullet shot still reaches a high intensity of -30db in this region. From this we can deduce that it is this lower frequency sound that is particular to the sonic quality of the rubber-coated bullet. This is perhaps because the rubber bullet is inserted into the end of the barrel and has a different system of propulsion than live fire (see weapons chapter). This low frequency sound specific to rubber coated bullet gunfire further corroborates the distinction in sound between live ammunition fired through a rubber bullet extension and the gunfire of rubber coated bullets.
- Finally, we compared the regular live, un-suppressed gunfire (shot 1) with the live ammunition suppressed by the rubber bullet extension (shot 2) and the live ammunition suppressed by the silencer (shot 4). What is observable in this comparison is that both extensions suppress the muzzle blast noise across the entire frequency spectrum. Furthermore, it is evident that the rubber bullet extension, to a much lesser intensity, has a similar effect on gunfire sound as a silencer does. A silencer is designed to cloak and disguise the sound of live ammunition in order to not alert people in the vicinity to the sound of live gunfire. The rubber bullet extension also suppresses the sound of live ammunition and to a lesser extent than a silencer, this extension can be used to disguise the presence of live fire.