Extractor marks made by automatic and repeating firearms can frequently be matched and often very effectively, as shown in several of the accompanying photographs (Figs. 31 to 35). In repeating guns, the depth of the impressions will vary considerably, depending on the vigor of the operator. Some guns will give excellent repetitive extractor marks while others will not. A loose extractor will give trouble. Some guns will produce well-defined ejector marks, but they are usually not as useful as extractor marks. The development of these depends even more on the vigor with which the action of the gun is operated. In automatics the force of the action is naturally more uniform and the results are likely to be more uniform also.
Because of the commendable practice of unloading hunting rifles and shotguns at the close of each day's shooting, it is a frequent experience to find several extractor marks and ejector marks on the same evidence shell. Extractor marks may be important in cases where no suspect gun is found or in case the suspect denies ownership of the suspect gun. In a case investigated by the Wisconsin State Crime Laboratory a suspect denied ownership or any knowledge of a gun which laboratory tests showed was the gun which had been used in the commission of a crime. Unfortunately for the suspect, however, he inadvertently dropped two unfired rifle cartridges while being questioned. When these were examined it was found that they had extractor marks on their rims which matched those on the evidence shell, showing that they had been „worked through" the rifle in question (Fig. 36). If one finds extractor marks or ejector marks on the same shell that are distinctly different, indicating that they have been worked through different guns, further inquiry into the history of the shell is in order, otherwise an innocent man may be unjustly involved. It must also be remembered that many fired shells have been reloaded and will thus have more than one set of markings when fired again. In the case of shells fired in revolvers, in nonautomatic pistols, and in nonrepeating arms in general, extractor marks and ejector marks will rarely be found.
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