Introduction
The phenomenon of tandem bullets is rare but not unknown. A pair of bullets travel in tandem if the nose of one is in contact with the base of the other. The phenomenon is observed when a bullet gets lodged inside the barrel and receives a kick on its base by the nose of another bullet fired subsequently. The impact results in the transfer of kinetic energy. The striking bullet loses kinetic energy whereas the lodged bullet gains kinetic energy. If the striking impulse is significant then the lodged bullet is unseated and becomes free to move in the forward direction along with the striking bullet, as a single projectile. These bullets moving together inside the barrel emerge from the muzzle in tandem. They tend to follow the same trajectory, but only for a short distance because the two together form an unstable projectile. The bullets are thereafter separated and follow different trajectories.
If the tandem bullets hit the target before separation, a single hole of entry may be observed. If the bullets separate before they hit the target two entry holes on the same or on different targets may be observed. The phenomenon of two separate regular entry holes by a single effective firing can be established if the recovered bullets are identified as tandem bullets. The identification of tandem bullets thus plays an important role in arriving at significant forensic conclusions. The present paper describes physical evidence observed on tandem bullets fired through a revolver. The possibility of evaluating the physical evidence is discussed.
Method
In a criminal case the phenomenon of tandem bullets was observed while firing test cartridges through an improvised .32 revolver. The fired 7.65 mm jacketed bullets were found lying together in the bullet recovery box. The nose of one was in contact with the base of the other. The two fired bullets were separated and thoroughly examined for physical evidence.
On examining the bullet lying ahead, the exposed lead base was found to carry unusual deep indentations of regular shape and size.
They appeared to be similar to those of the propellant usually loaded in revolver cartridges. (Fig 1.)
Fig 1.Indentations on exposed lead base cavity.
The shape and size of the deep indentations on the lead base cavity were compared under the comparison microscope with those of the remaining propellant removed from the cartridge case which had fired the lodged bullet. They were found similar. This indicated that the indentations could have been caused by unburned and partially burned propellant particles. Besides deep indentations, the bullet was also found to carry small patches of striations on the inner periphery of the exposed lead base cavity.(Fig)
Fig 2. Striae patches on lodged bullet base periphery.
On examining the bullet found lying behind, it was observed that the exposed lead base cavity had neither deep indentations nor striation patches around the inner periphery. Instead, its base was found to be protruding outwards. The rearward protrusion of the lead core was compared with the base of a bullet of the same make and lot fired through the same .32 revolver. The fired bullet, not behaving as a tandem bullet , did not show reward protrusion of the lead core. The protrusion at the rear,thus, suggested that the bullet had hit sufficiently hard at the nose to experience an impulse in the rearward direction.
Discussion
When a cartridge is fired , the propellant convertes into gases and a high pressure is developed inside the barrel. The bullet is forced down the bore and finally emerges from the barrel. If the combustion is incomplete, a low pressure may be developed and the bullet may get lodged inside the barrel. The partially burned and unburned powder particles may stick to the lead base cavity of the jacketed/unjacketed lodged bullet. The probability of propellant particles sticking to the flat metal based bullet is remote. If the lodged bullet is not removed and another round is fired then the base of the lodged bullet is hit by the nose of the subsequently fired bullet. The nose impact may result in hitting the unburned/partially burned propellant particles sticking to the exposed lead base cavity causing deep indentations. Further, the nose of the striking bullet coming in sliding contact with the portion of the base cavity may cause patches of striations on the inner periphery. The lodged bullet also momentarily restricts the forward motion of the striking bullet. Thus the nose of the striking bullet ,on hitting the base of the lodged bullet experiences an opposite impulse. The impulse, if sufficient, may result in protrusion of the base of the striking bullet.
From the aforesaid discussion it is apparent that the observed physical evidence on tandem bullets was in agreement with the plausible theoretical considerations. Evaluation of the physical evidence proved helpful in assessing lodged and striking bullet moving in tandem.
