Diameter of cranial gunshot wounds as a function of bullet caliber

Determination of bullet caliber becomes increasingly important in homicides where the bullet is missing. In cases with entrance wounds to bone that are circular and well defined it may be tempting to measure the defect and offer suggestions about bullet caliber. For this reason, the relationship between wound diameter and bullet caliber was examined using cranial bones from autopsy cases. The minimum diameter of 35 cranial wounds produced by .22, .25, and .38-caliber bullet was measured. The relationship of minimum wound diameter to bullet caliber was examined using a one way analysis of variance. Fisher's least significant difference test revealed no significant difference between .22-caliber and .25-caliber wounds, while the .38-caliber wounds were significantly different (P < .001) from .22-caliber and .25-caliber wounds. Variation in wound size resulting from such factors as bullet shape, surface treatment, strength characteristics, loss of gyroscopic stability, intermediate targets, tangential impacts, and existing fractures are discussed. Also, the large variety of calibers available are noted as complicating the prediction of caliber from wound size. In view of these factors caution is recommended in any attempt to determine precise bullet caliber from the minimum dimensions of the cranial gunshot entrance wound.