Measurements of land widths in new guns of same make and model

It has long seemed desirable to the writer to make a study of the land impressions made on (A) plain lead bullets and (B) metal-cased bullets which had been fired from the same guns. It also seemed desirable to make a study of the variations in land widths which occur in the same make and model of guns made by a reputable manufacturer. The writer was furnished sets of bullets, both plain lead and metal cased, which had been fired from the same guns. These guns were the .38 Spl. Smith and Wesson, Military and Police Model, and they had never been fired since leaving the factory. They were the property of the Berkeley Police Department. For the details concerning the guns and ammunition used and the conditions under which these tests were fired see Table 5 and supplementary notes.

Because a new gun has rifling which is not worn, it is to be expected that the imprints of the lands on the fired bullets would be wider and that they would be more cleanly cut than would be the case for a much-used gun. It also is to be expected that a metal-cased bullet would show more cleanly cut land impressions than those made on a lead bullet, because of the softness of lead in comparison to metal-cased bullets. In the case of a new gun, or one having undamaged rifling, it would be expected that the width of the land impressions would be the same on lead and metal-cased bullets if normal powder pressures were used. The first assumption is verified, but the last one seems to be only approximately true.

Table 5 shows that usually the widths of land impressions on lead bullets are slightly narrower than those found on metal-cased bullets fired from the same gun. In no case were they wider. Since the differences are all in the same direction, it is believed that they are real and are not the result of error in measuring.

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