Berryman et al. [
5], Ross [
6], and Paschall and Ross [
7] studied calvarium samples from forensic collections, with defects caused by bullets of a known caliber. The notion of a “caliber” in the three studies was implicitly defined as the nominal bullet diameter, or rather a range of bullets with the same diameter, without reference to specific cartridge designations. The size of each defect was compared to the diameter of the caliber group to which the causative bullet was assigned. The different caliber groups will be referred to as .22, .25, .32, and .38 in this review, following the nomenclature of the three studies. Berrymann et al. [
5] measured the maximum diameter size of 16, 8 and 11 defects, known to be caused by .22, .25 and .38 caliber bullets, respectively. The measurements were performed with a caliper on the outer rim of the entrance side of the defects. The mean diameter of the defects caused by the .22, .25 and .38 bullets was measured to be 36%, 12%, and 21% larger than the respective bullet diameters. Some individual measurements in the .38 caliber group where measured to be smaller. This was not the case in the .22 and the .25 caliber group. Ross [
6] measured 37, 5, 6, and 25 defects, known to be caused by .22, .25, .32, and .38 caliber bullets. The mean minimum diameters of the defects caused by the .22, .25, .32, and .38 bullets were measured to be 18%, 6%, 14%, and 22% larger than the respective calibers. Some individual defect measurements in the .25, .32, and .38 caliber groups were measured to be smaller than the calibers of those groups. This was not the case in the .22 caliber group. The study by Ross indicated that the defect diameter is influenced by not only the caliber of the bullet but also by the thickness of the bone, in the sense that bullets produce larger defects in thicker bone. Paschall and Ross [
7] studied a total of 169 samples, 68 of which were studied by the authors directly and 101 of which were taken from the literature [
9]. Of all defects, 77 were caused by .22 caliber bullets, 40 by .32 caliber bullets, and 52 by .38 caliber bullets. The authors tried to classify the samples by their minimum defect size to the known caliber group. The overall misclassification rate was 41%. A study of an eighteen sample sub set indicated that the difference in bullet defect diameter is influenced by not only the caliber of the bullet and bone thickness, but also by bone mineral density (BMD) in the sense that bullets produce larger defects in bone with a higher BMD. The influence of BMD on defect size was found to be larger than that of bone thickness.
Kuhl and Janssen [
8] fired 96 bullets orthogonally (90° in all directions) at heads of fresh human remains, still containing a brain, some with and some without overlying soft tissue. The bone around each bullet defect was sawed out, soaked for 14 days in a 4% formalin solution and air-dried. A further 113 bullets were fired orthogonally at fresh human calvariums, 18 of which had the overlying soft tissue removed before shooting. The thickness as well as the BMD of the samples was measured. The authors used cartridges of six different calibers in their study. The calibers used in this study were defined as specific cartridge designations instead of caliber groups, as was the case in the aforementioned studies [
5‐
7]. The used .32 Auto, .380 Auto and 9 mm Luger cartridges were loaded with full metal jacket bullets. The .32 Long Colt, .38 S&W and .38 Special cartridges used were loaded with lead bullets. The bullet defect size was measured with a conical (tapered) shaft, placed in each defect. The diameter of the cone at the position it stuck in the defect was measured. The diameters of the defects were found to be about equal in the samples taken from the heads and taken from the calvariums. The mean diameters of the defects caused by the .32 Auto, .380 Auto, and 9 mm Luger full metal jacket bullets were 6% larger, about equal in size, and 3% smaller than the original bullet diameters, respectively. The mean diameters of the defects caused by the .32 Long Colt and .38 S&W lead bullets were measured to be 5–9% and 8% larger than the original bullet diameter, respectively. The mean diameter of the defects caused by the .38 Special lead bullets fired at heads and unmacerated calvariums were 24% larger than the original bullet diameter. The mean diameter of the defects caused by these bullets in the 18 samples without overlying soft tissue were measured to be only 16% larger than the original bullet diameter. The study by Kuhl and Janssen, as did the study by Ross [
6], indicated that bullets have a tendency to produce larger defects in thicker bone and, as found by Paschall and Ross [
7], have a tendency to produce larger defects in bone with a higher BMD.