Sympathetic Discharge of Rimfire Firearms

In cheap .22 rimfire revolvers, "sympathetic" discharges may occur on firing. "Sympathetic" discharge occurs when, on firing a revolver, there is not only discharge of the cartridge stuck by the firing pin but also of a cartridge in an adjacent chamber. Such multiple discharges were quite common in percussion revolvers when a spark from a discharging round would ignite the black powder in other cylinders.

In sympathetic discharge of .22 rimfire revolvers, discharge of a cartridge by the firing pin causes recoil of the cylinder against the frame with resultant compression of the rim of a cartridge case in an adjacent chamber between the frame and cylinder, producing a second discharge (Figure 10.4). As this chamber is not aligned with the barrel, no rifling will be imparted to the bullet. In addition, the inner surface of the bullet will be partially shaved away by the frame of the revolver as the bullet travels forward. Sympathetic discharge can occur only in rimfire cartridges, not in centerfire cartridges, because of the centrally located primer in the latter type of cartridge.

In a case seen by the author, a young male was shot during an argument on a bus. There was a penetrating gunshot wound of the right cheek with an apparent graze wound of the right shoulder. The bullet recovered from the head was a .22-caliber rimfire bullet with rifling marks on its sides. The

Pictures Bullet Graze Wounds
Figure 10.4 Sympathetic discharge of .22 rimfire revolver. (A) The weapon has just been fired; (B) a bullet has emerged from the barrel; (C) a second bullet has come out the left side of the cylinder and is approximately 1 in. ahead of the barrel. The arrow indicates where the bullet emerged from.

bullet that caused the graze wound was found loose in the clothing. Examination of this bullet showed shortening of its length (from base to tip), absence of rifling, one side sheared off, and an expanded (flared-out) base having a granular pock-marked surface resulting from impaction of powder grains (Figure 10.5). This appearance of the bullet is classical for sympathetic discharge of a weapon. Examination of the weapon confirmed the tendency of the gun to sympathetic discharge.

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