How Did Lincoln Die?

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Ford’s Theatre Museum, where the weapon is currently kept, gave me a detailed description of the gun that Booth used to assassinate President Lincoln. It is a single-shot muzzleloading Philadelphia derringer with a percussion cap. Its total length is 5 27/32 inches, but the barrel is only 1 15/16 inches long. The interior diameter of the barrel is 0.4375 inch, making the gun a .44-caliber pistol (caliber refers to the barrel and/or bullet diameter in inches). The derringer shot a round lead ball. Usually a gun fires a bullet or ball of approximately the same caliber, but the pathological examination of the ball that killed Lincoln suggests that Booth used a .41-caliber ball in his .44 derringer.

The National Museum of Health and Medicine currently owns the ball that killed Lincoln. On April 6, 1971, the ball was examined. It weighed 6.314 grams and was found, by spectroscopy, to be principally lead. Its weight was not the same as at the time Booth shot it, for three reasons: the lead had corroded, and the corrosion was easily rubbed off in handling the ball; it had a small hole drilled into it prior to 1941 for mounting at an exhibition; and most significantly, part of the ball had been broken off by the skull when it entered the President’s head. This fragment was found during the autopsy but was later lost. The ball was flattened by the impact of the shot; in 1971 it was measured at 13.3 mm in diameter at its widest and 12.1 mm at its narrowest point and was 7.2 mm from front to back.

 
 

The most widely accepted current theory that attempts to describe the extent of tissue damage incurred by a missile states that its wounding capacity is proportional to its kinetic energy, which may be calculated with the formula: KE = ½ mv 2 . In other words, the kinetic energy of a missile is proportional to the missile’s mass times the square of its velocity. The kinetic energy, and therefore the wounding capacity, of a bullet is much more dependent on its velocity than on its mass. If a bullet’s mass is doubled, its kinetic energy is doubled; if a bullet’s velocity is doubled, its kinetic energy is quadrupled.

The derringer fired by Booth had a very low muzzle velocity—around four hundred feet per second, which is about that of most of today’s air guns. To calculate the ball’s kinetic energy, the only further measurement needed is its mass. Since the ball was weighed after a significant amount of its volume had been lost, it seems sensible to estimate its original mass using the density of lead and the volume of a .41-caliber sphere, which would have been 6.7 grams.

From this it can be calculated that the kinetic energy of the missile that killed Lincoln was 36.7 foot-pounds. Today this magnitude of kinetic energy is associated with guns of a much lower caliber. A .22-caliber short revolver, for example, produces approximately 48 foot-pounds of kinetic energy. A pathologist describing the wound of a twenty-year-old male who shot himself in the head with this type of gun noted that the bullet entered the brain in the right temporal lobe and perforated the left parietal lobe before lodging in the left occipital region. The bullet’s track was straight and cylindrical, tapered at the entrance and lodgment areas, and about three centimeters wide in the middle. This wide area is the result of cavitation, a phenomenon common to missile wounds. Lower-velocity bullets will normally produce little or no cavitation, while high-velocity ones transfer more of their kinetic energy to the tissue and produce large temporary and permanent cavities. A temporary cavity is formed when the missile’s kinetic energy separates the soft tissue around where it strikes, producing a wide opening for a fraction of a second before the tissue recedes back toward its normal position. If the tissue does not recede completely, a permanent cavity is formed.

The derringer had a very low muzzle velocity— around four hundred feet per second, about that of today’s air guns.

The shape and size of this cavity also depend on variables other than kinetic energy, such as yaw—the wobbling motion of a bullet—and the effect of secondary missiles that form when the bullet’s kinetic energy is transferred to bone, which fragments and itself becomes projectiles. When the bullet enters tissue, it chisels out a cavity much larger than its own diameter. A ball cannot produce yaw because it has no longitudinal axis to wobble on, and no secondary missiles were formed in Lincoln’s injury because, other than entering the occipital bone, the ball encountered only soft brain matter. The occipital bone that was hit was driven like a plug and found in the autopsy about two and a half inches down the missile track. The hole made in the bone, wrote a witness to the autopsy, “was as cleanly cut as if done with a punch.” The absence of yaw and secondary missiles combined with the ball’s low velocity should have rendered the effect of cavitation in Lincoln’s wound minimal, and indeed, the autopsy report seems to indicate the ball’s having made a fairly clean, narrow track.