A study of the reproducibility of the measurement

The data recorded in Table 4 resulted from a study of the widths of land impressions on a series of lead bullets fired from a group of seventeen .38 Spl. S&W revolvers, all of which had seen extensive use prior to and after their purchase by the Berkeley, Calif., Police Department.*

*These bullets were submitted by Mr. A. A. Biasotti, formerly with the Wisconsin Crime Laboratory and now at the Laboratory of Criminalistics, Office of the District Attorney of Santa Clara Co., San Jose, Calif.

The guns are listed as Nos. 2 to 18 in the order in which they were fired. For the details concerning the guns and ammunition used and the conditions under which these tests were fired see Table 4 and supplementary notes. As was expected, since all of these were used guns, some of the bullets were not in suitable condition for measurement. Some of these guns had evidently seen much use-and, possibly, abuse. Measurements were made on those bullets which had at least four measurable land impressions.

Satisfactory measurements could not be made on bullets fired from guns 13, 14, and 17, because the rifling did not leave sufficiently well-defined land impressions.

By reference to the measurements given in Table 4, it is clear that accurate measurements of the widths of land impressions on a fired bullet can be made by the procedure developed, provided the bullets have been fired from guns that are in reasonably good condition and have not been damaged in the process of being collected. It seems fair to conclude that the variation in reproducibility of a series of measurements is not greater than ±0.001 inch, and usually it is less.

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