Audio forensics is the one issue in the field of forensic science to investigate the crime committed by using firearms. The gun blast gives us important information of its caliber leading to identifying the firearm used by the criminal in the crime scene. It can be recorded by an audio-recorder under various conditions. In recording process, the gunshot blast is affected by many factors, including the type and the caliber of firearm, the location of shooter, wind speed, temperature, sound reflection and reverberation, the type and the quality of bullet, the direction of the firearm, the shooting position, and the orientation or the location of the sound recorder. Those features make the firearm identification from the gunshot blast more difficult. The audio forensic gunshots have been investigated. The work[1] reported a survey of audio forensic gunshot. The gunshot audibility, gunshot signature and gunshot timing “were” briefly presented.[1] Some works [2,3] described some acoustical characterization of gunshots. They also reported about directional aspects of forensic gunshot recordings. [3]. The work[4] reported the barrel length aspects of audio forensic. The gun with the longer barrel produced lower amplitude of gunshot sound than that of the shorter barrel. This paper presented a firearm identification method from the gunshot blast. We proposed a firearm identification method
using the Fourier cosine coefficients of the autocorrelation functions of gunshot sound signal. II. DATA GATHERING A. Firearm testing data set Eight firearms as shown in Table 1, five semi-auto pistols, two revolvers, and one rifle (Lever-action) with different barrel lengths, were used in the gunshot sound recording. Two semi-auto guns were categorized as the single-action pistols while the other three were double-action pistols. All of them are operated by the previous shot fired, the spent case ejected, and a fresh cartridge from their magazines loaded into the chamber to complete the cycle. This continues until their magazines are empty. The trigger of the single-action a semiauto can be pulled after its hammer is cocked whereas the one of the double-action pistol can be pulled as the hammer is in either cocked or lowered position. A revolver has multiple chambers (a cylinder) but a single barrel, and the two revolvers used in the experiment were double-revolvers with the 6-shot cylinders. Their trigger mechanisms are the same as those of double-action semi-auto pistols. After the revolvers are fired, however, the empty cases are still kept until their cylinders are opened to eject them. A rifle cartridge contains a bullet and explosive compound forming a complete round, and being chambered into the barrel. When the trigger is pulled, the firing pin strikes the primer of the cartridge, then ignites the gunpowder. Since the powder is an explosive compounds, it propels the bullet forward along the grooved barrel. The spent cartridge is then ejected before the next round is chambered and ready to fire.