Reproducibility And Individuality Of Characteristic Marks On Fired Cartridge Cases From Five Chinese Norinco Qsz-92 9×19mm Pistols

The scientific reliability of firearms identification has been challenged by the Daubert,like most forensic science evidence,especially the reproducibility and individuality of firearms marks.Firearm examiners have performed many studies to prove these two themes.However,in previous studies,the variations of marks are mainly evaluated by firearm examiners through microscopic examination,which is a time-consuming and subjective process.In this paper,we used an automated ballistic identification system Evofinder~?to study cartridge cases fired from five Chinese Norinco QSZ-92 9×19mm pistols.Each pistol fired 3070 consecutive shots.The first 20 cartridge cases were all introduced into the system.From the 21st until the 3070th shot,every ten cartridge cases were collected and one random sample of each group was introduced as the 30th,40th,...,3070th round.Thus,we introduced 325 specimens for each pistol and established a database of 1625 specimens.Both onscreen examination and automatic correlation are used to examine the reproducibility.In the onscreen examination process,it is possible for firearm examiners to positively identify the first cartridge to the 500th,1000th,1500th,2000th,2500th,3000th cartridge.In the automatic correlation process,the first cartridge of each firearm is separately performed correlation against the database.It is found that the similarity score for match objects change slightly as the shot number increases,indicating slight variations of marks.However,these variations have not prohibited the Evofinder?system to make correct correlation and rank100%of the known match objects on the top of the correlation list by either firing pin impression or breech face mark.Thus,reproducibility is proved statistically and objectively.We used the first and every 100th specimen of each firearm to start correlations in the database and analyzed the results,especially the results of specimen 0001,1000,2000,3000.Consequently,specimens fired closer in sequence to the specimen under examination had higher similarity scores.In boxplots,the boxes of known match specimens were much higher than boxes of known non match specimens.The Evofinder~?ranked nearly all known match specimens in the first position of either firing pin impression list or breech face mark list.In conclusion,the two marks changed over 3070 consecutive shots and cartridge cases of nearer shot numbers were more similar.However,the variations of marks from the same firearm have not exceeded the differences between marks of different firearms and have not hindered the Evofinder~?to make nearly 100%correct correlations.The results of our study are in agreement with the work conducted previously and strengthen their findings statistically.The reproducibility,variation and individuality of firearms marks are visible in our results.This work can help firearm examiners to better understand and use the correlation result of the Evofinder~?system,especially the pure value of similarity score,the gap of similarity scores and their relationship.